Emotions and Dog Bites: Could Predatory Attacks Be Triggered by Emotional States?

Abstract

Dog biting events pose severe public health and animal welfare concerns. They result in several consequences for both humans (including physical and psychological trauma) and the dog involved in the biting episode (abandonment, relocation to shelter and euthanasia). Although numerous epidemiological studies have analyzed the different factors influencing the occurrence of such events, to date the role of emotions in the expression of predatory attacks toward humans has been scarcely investigated. This paper focuses on the influence of emotional states on triggering predatory attacks in dogs, particularly in some breeds whose aggression causes severe consequences to human victims. We suggest that a comprehensive analysis of the dog bite phenomenon should consider the emotional state of biting dogs in order to collect reliable and realistic data about bite episodes.

Full text

animals
Viewpoint
Emotions and Dog Bites: Could Predatory Attacks Be Triggered
by Emotional States?
Serenella d’Ingeo 1, *,† , Fabrizio Iarussi 2, † , Valentina De Monte 3, Marcello Siniscalchi 1, Michele Minunno 1
and Angelo Quaranta 1


Citation: d’Ingeo, S.; Iarussi, F.;
De Monte, V.; Siniscalchi, M.;
Minunno, M.; Quaranta, A. Emotions
and Dog Bites: Could Predatory
Attacks Be Triggered by Emotional
States? Animals 2021,11, 2907.
https://doi.org/10.3390/ani11102907
Academic Editor: Mark J. Farnworth
Received: 8 July 2021
Accepted: 6 October 2021
Published: 8 October 2021
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
1Animal Physiology and Behavior Unit, Department of Veterinary Medicine, University of Bari Aldo Moro,
70100 Bari, Italy; marcello.siniscalchi@uniba.it (M.S.); m.minunno79@libero.it (M.M.);
angelo.quaranta@uniba.it (A.Q.)
2Veterinary Section, Department of Emergency and Organ Transplants, University of Bari Aldo Moro,
70100 Bari, Italy; fabrizio.iarussi@uniba.it
3Private Practitioner, 70121 Bari, Italy; valedemo@inwind.it
*Correspondence: serenella.dingeo@uniba.it
† These authors contributed equally to this work as first authors.
Simple Summary:
Dog bites are a worldwide problem that have severe consequences for both the
animal and the victim involved in the incident. Epidemiological studies have analyzed the victim
features, the characteristics of biting dogs and the context in which attacks occur. Little is known
regarding the role of emotions in predatory attacks toward humans and conspecifics in dogs. This
paper aims at proposing the potential involvement of emotions for the expression of predatory motor
patterns. It is suggested that the reporting of dog biting episodes needs to consider this crucial factor,
which is fundamental for providing a realistic and reliable picture of the dog bite phenomenon.
Abstract:
Dog biting events pose severe public health and animal welfare concerns. They result
in several consequences for both humans (including physical and psychological trauma) and the
dog involved in the biting episode (abandonment, relocation to shelter and euthanasia). Although
numerous epidemiological studies have analyzed the different factors influencing the occurrence
of such events, to date the role of emotions in the expression of predatory attacks toward humans
has been scarcely investigated. This paper focuses on the influence of emotional states on triggering
predatory attacks in dogs, particularly in some breeds whose aggression causes severe consequences
to human victims. We suggest that a comprehensive analysis of the dog bite phenomenon should
consider the emotional state of biting dogs in order to collect reliable and realistic data about
bite episodes.
Keywords: dog bite; aggressive behavior; predatory behavior; emotions; physiology
1. Introduction
Dog bites are a serious worldwide problem. The consequences for human health
include physical injuries, transmission of zoonosis and psychological trauma [
1
]. The
issue of dog biting also has a significant impact on dog welfare. It is a common cause
for abandonment, relocation to shelter and euthanasia [
2
,
3
]. Dog-related human fatalities
are rare events (0.01% of all dog bites) but they are the most serious consequence of dog
attacks [
4
]. More than 300 individuals died from dog attacks in the US from 1979 to 1998 [
5
].
In France, 20 bite-related fatalities have occurred in the past 30 years [
6
]. In Italy, from 1984
to 2020, 58 individuals died from dog attacks ([
7
]—data from media reports of 2009-2020).
In recent years, many studies have been carried out in order to understand the
epidemiology of dog bites. Several authors have investigated the victim features, the
characteristics of biting dogs and the context in which attacks occur [
3
,
8
–
10
]. This led to
the definition of a dog bite as a multifactorial phenomenon, whose expression is regulated
Animals 2021,11, 2907. https://doi.org/10.3390/ani11102907 https://www.mdpi.com/journal/animals

Animals 2021,11, 2907 2 of 7
by genetic, physiological, developmental, environmental and social factors [
4
]. According
to the clinical and behavioral assessments of biting dogs, the attacks toward humans are
most commonly caused by fear and anxiety (77%) [
11
–
14
], suggesting that dogs’ emotions
and their relationship to humans are crucial components of the biting phenomenon. Recent
studies have demonstrated, indeed, that dogs are able to interpret human emotional
states and regulate their behavior accordingly [
15
–
18
]. Therefore, their influence on the
development of dog biting events needs to be further and deeply investigated.
This paper aims at analyzing the potential influence of emotions on dog aggressive
behavior, with a specific focus on the importance of this factor for the expression of
predatory aggression, particularly in some breeds.
2. Emotions and Aggressive Behavior in Dogs: The Role of Emotions in Biting Episodes
Dog aggressive behaviors are broadly divided in two main categories: predatory be-
havior and affective aggression [
19
]. They mainly differ in their aims and neural regulation.
Predatory motor patterns are part of feeding behavior: they aim at obtaining food by killing
and consuming prey [
19
–
21
]. In dogs, the predatory sequence includes different motor
patterns (more generally defined as predatory behaviors): orienting towards prey, eye
stalk, chase, grab bite, kill bite (or head shake), dissection and consumption [
20
]. In the
literature, it is reported that dogs might engage in predation toward both conspecifics and
heterospecifics (e.g., humans [
19
]). This behavior is widely described as “predatory aggres-
sion”. It has been considered a non-emotional or non-affective type of aggression, where
communication between subjects is absent and the sympathetic arousal is low
[19,22–24]
.
Conversely, social/affective aggression (which might be offensive and defensive) has a
strong emotional and communicative component and is accompanied by a significant
sympathetic activation [
19
,
23
,
25
]. Social aggression serves to increase the distance be-
tween subjects and eventually avoid/control negative outcomes through the expression of
threatening behaviors (e.g., growling, posturing, snapping) [
19
,
20
,
23
]. Affective aggression
is triggered by transient emotional states (e.g., frustration, fear, irritability, anxiety) [
19
].
Besides the differences in their scopes, the neural regulation of predatory and affective
aggression also involves distinct structures of the hypothalamus: the ventro-medial hy-
pothalamus controls affective aggression, whereas the lateral hypothalamus regulates
predatory behavior [
19
]. Both of them receive inputs from the limbic system, specifically
from the amygdala [23,26].
Recently, some authors challenged the inclusion of predatory attack into the general
category of aggressive behavior, which includes, for instance, play-related aggression,
territorial aggression, defensive aggression and fear-related aggression [
23
,
26
–
29
]. Indeed,
aggression is defined as “threats, postures, or harmful actions directed towards another
individual. Aggression is a form of communication, where aggressor is attempting to
establish greater social distance between himself and the target of his aggression” ([
20
],
p. 2). It is also “one component of agonistic behavior that serves to regulate individuals’
ability to compete for various resources (food, shelter, territory, mates, social status)” [
4
].
Moreover, it has been defined as “an appropriate or inappropriate threat or challenge that is
finally resolved in an act of fight or disengagement [
29
,
30
]” as well as “a behavior or model
of threatening and confrontational behaviors used to resolve a conflict, which is finally
settled through confrontation or backing/withdrawal [
30
,
31
]”. In predatory “aggression”,
which includes behaviors aimed at capturing and killing prey, the intent to communicate
and challenge other individuals as previously described is lacking. We therefore believe
that it would be more appropriate to refer to predatory behavior causing lesions to other
individuals as “predatory attack” rather than predatory aggression. We will refer to this
phenomenon by using these terms.
While the involvement of emotions in the expression of social aggression is clearly
described and broadly recognized, their influence on predatory attacks was at first excluded
(as reported above). However, available and recent evidence suggests that emotional states
might have a role in triggering predatory attacks in dogs. Some authors showed that

Animals 2021,11, 2907 3 of 7
predatory attacks, which usually cause severe injuries or the death of the victims, could
be influenced by emotional factors, such as anxiety or frustration, which modulate their
expression [
19
,
24
]. Among the main causes of dog killing aggression toward humans and
conspecifics is an insufficient socialization with these species, and previous unpleasant or
traumatic experiences (the “aggressors” were previously victims of a conspecific aggression
or attack) could play an important role [
24
,
25
]. They might lead dogs to experience
emotions such as fear, anxiety and frustration during social encounters, which increase
the subjects’ emotional tension (stress) and might consequently trigger the expression of
predatory behaviors [
25
]. Frustration, indeed, is generally triggered by unpredictable and
uncontrollable events that elicit contrasting emotions and inner conflicts [
19
]. It has also
been previously related to the engagement of the reactive aggression (RAGE) system [
32
],
which has been anecdotally described for backyard dogs due to the presence of barriers
or any forms of confinement [
33
]. It causes the increase in subjects’ arousal, which is
functional for identifying an adaptive response when facing an unexpected event [
19
].
However, when the arousal and frustration levels are too high, the emotional tension
might persist and lead to the expression of behaviors in an intense and dysregulated
way. As a consequence, the subject could engage in behaviors aiming at restoring the
emotional homeostasis.
An important role for the regulation of stress-related behavior is played by dopamine.
It has been found that its concentration decreases in the dopaminergic mesolimbic system
(“reward system”) in response to stress, arousal increase and in the presence of environ-
mental alarming signals [
34
]. Dopamine has a key role for the coordination and regulation
of motivated behaviors: the reward system is activated when motivations are fulfilled.
This leads dogs to experience pleasant emotions and the achievement of pleasure [
35
]. We
can therefore hypothesize that, when experiencing an emotional conflict (i.e., frustration)
or an increase in their emotional tension, subjects could engage in highly gratifying and
motivated behaviors for restoring their emotional homeostasis by the activation of the
reward system. The behaviors expressed might not be adaptive per se (i.e., removing the
stressor that generated the conflict) but they might only have the aim of decreasing the
emotional tension in individuals.
Among the highly motivated behaviors, predatory motor patters are particularly
rewarding for dogs. Their expression, indeed, maximally activates the reward neural
centers [
24
] and generates a pleasant hedonic experience, which is analogous to the satis-
faction of hunger and thirst [
19
]. It could be possible, therefore, that dogs could engage in
predatory behaviors when experiencing stress, frustration and an arousal increase in order
to reach pleasure and gratification, which could subsequently reduce the state of emotional
tension generated by a stressor.
Evidence for an association between the arousal increase and the expression of preda-
tory attacks has also been shown in a recent study. Schilder and colleagues [
25
] found that
dogs, which previously showed predatory attacks toward other conspecifics, expressed
high vigilance during the walk with the owner even before meeting with another dog. The
subjects’ arousal significantly increased at the sight of a conspecific or when they reached a
place where they expected to meet another dog (i.e., anticipation).
In light of this, we could hypothesize that predatory attacks could be triggered both by
the movement of the victim (i.e., prey) but also by a state of emotional tension, which might
be “discharged” through the expression of highly rewarding predatory behaviors. This
could make the treatment of this specific behavioral problem very difficult, as previously
reported [24].
However, we cannot rule out the possibility that the arousal increase registered before
the expression of predatory attack could be related to the anticipation of positive outcomes,
i.e., food consumption. Therefore, further studies are needed to clarify the cause of subjects’
arousal increase in order to understand its valence (i.e., positive or negative) and to measure
its intensity, by evaluating dog behavior and other physiological parameters (e.g., heart
rate increase by ECG wireless systems; body and facial surface temperature [
16
–
18
,
36
]).

Animals 2021,11, 2907 4 of 7
Similarly, since frustration has been implicated in the expression of displacement and
repetitive behaviors [
37
–
39
], it could be possible that one or more phases of the predatory
attack triggered by frustration could be an expression of displacement activities, which are
usually normal behaviors expressed in an inappropriate context and time [20].
It has been shown that predatory attacks could be more easily triggered in subjects
showing predatory motor patterns towards all type of animal species [
24
,
25
]. The genetic
selection of different breeds has a deep influence on dog phenotypical and behavioral
features. Humans modified and differentiated the motivations of different breeds according
to their role in human society [
23
]. For some breeds, humans selected and emphasized
specific phases of the predatory sequence for their work, increasing the likelihood of their
expression and their rewarding value. Headers (including border collies), for instance,
were selected for conducting herds by causing them no injuries. The behavior of stalking
and chasing was hypertrophied while the bite (both grab and kill bite) was diminished.
Similarly, livestock guardian dogs (such as the Maremma sheepdogs) were selected for
the absence of any predatory behavior directed toward the sheep; therefore, the entire
predatory sequence was “quieted” [
20
,
40
,
41
]. Different breeds were also selected for
dog fighting, which was highly popular in the 1800s [
42
]. They include “pit bull” dog
types, bull terriers, mastiffs and bull dogs [
43
] (later referred to as “fighting dog breeds”),
which show similar phenotypical and behavioral characteristics. In particular, the bite
behaviors belonging to the predatory motor patterns (i.e., sustained grabbing, holding,
shaking, tearing) were selected and emphasized in order to produce the maximum damage
to the dog opponent during fighting [
44
]. Since genetic selection has also acted on the
functionality of the nervous system by affecting the distribution of dopamine receptors [
23
],
it is likely that the expression of the selected hypertrophied behaviors would significantly
increase the dopamine levels in the reward centers and consequently intensely gratify
dogs. Therefore, it could be possible that dogs belonging to the breeds where specific
phases of the predatory sequence were hypertrophied may engage in predatory behaviors
during stressful situations in order to restore their emotional homeostasis and experience
pleasure. In other words, when a border collie is experiencing a high arousal increase
(related to stress or frustration) it could be likely that it engages in chasing objects or
other individuals, whereas “fighting dog breeds” might direct predatory bites towards
objects, conspecifics and even humans. This might pose a severe risk for humans and
public health. Indeed, pit bulls (even though they do not belong to an officially recognized
breed) are frequently involved in biting episodes worldwide and particularly in the US
and UK [
45
,
46
]. “Fighting dog breed” (including pit bulls) selection also fixed behavioral
and personality characteristics that were useful their work [4,44]:
−
Gameness: high perseverance until the goal is reached, causing the lack of sensibility
toward the other subject’s surrender signals;
−
Low inhibition for fighting: high reactivity to minimum threats (moving or non-
moving stimuli) activates behavioral responses until the complete exhaustion or
death;
−Low sensitivity to pain;
−Scarce communication, which enhances the unpredictability of the attack.
The lack of prodromal warning signals (e.g., growl, freeze, snap, directed and pro-
longed gaze) preceding the attack, indeed, is frequently reported by human victims
[4,47–49]
.
Breeding has also caused a genetic vulnerability due to a greater sensitivity to threatening
stimuli [
25
], which might be related to a different perception of environmental and social
stimuli [23].
It is possible therefore that an environmental/social stressor may cause a significant
increase in these breeds’ emotional tension (due to their high sensitivity) that could be
“discharged” by the expression of the predatory bite, which produces a deep sense of
gratification and pleasure in these dogs.
The sensitivity and vulnerability to stress, along with the high perseverance and
the lack of responsiveness to the opponent’s reactions, as well as the high gratification

Animals 2021,11, 2907 5 of 7
produced by the expression of the kill bite (aiming at inflicting the maximum damage to
the victim), make the attack of “fighting dog breeds” particularly dangerous, and raise
serious issues for public health.
Although this might explain the high prevalence of severe/fatal attacks of pit bulls
reported by the recent literature and media, some important considerations about this phe-
nomenon are needed. Firstly, numerous mixed-breed dogs are referred to as pit bulls on the
basis of their phenotypical similarities. It is widely reported, indeed, that the ability of the
public, the victims and official authorities to correctly identify dog breeds and dangerous
dogs is notoriously faulty [
50
,
51
]. This could lead to a significant overestimation of the
involvement of pit bulls in biting events. It could also be affected by the general lack of
demographic data regarding the breed representation within the general registered dog
population [
4
,
44
]. Therefore, despite the removal of “fighting” dogs from the breeding of
officially recognized breeds, which aims at mitigating the personality characteristics of
these dogs, the lack of reliable data about the involvement of these dogs in biting episodes
makes the evaluation of the influence of genetic factors particularly difficult [
44
]. “Fighting
dog breeds”, indeed, have also been selected for stability and tractability with people [
52
]
and make the dogs belonging to officially recognized breeds suitable as household com-
panions [
42
]. However, detailed data are instead necessary in order to assess and monitor
the long-term effect of the current rebreeding process of officially recognized “fighting dog
breeds” on their personality traits.
In light of this, and considering the multifactorial nature of dog bites, it is crucial that
the behavioral assessment of biting dogs is carried out by behavior specialists in order
to evaluate the different motivations and emotions that trigger aggression, as well as the
influence of individual personality and the social and environmental living conditions
on the expression of such phenomena. This specific and comprehensive evaluation is
necessary for a correct management and application of a therapeutic plan that needs to be
individual oriented.
3. Conclusions
Emotions play a pivotal role in the development and expression of dog behavior,
including aggression and predatory attacks towards humans or conspecifics. Therefore, a
comprehensive analysis of all the factors involved in the onset of biting events should not
disregard the evaluation of dog emotional state, as well as the relationship with the owner
and the member of the familiar group, as well as the management and the living conditions
of the animal. This would allow veterinarians and researchers to collect a realistic and
reliable picture of the dog bite phenomenon.
Author Contributions:
Conceptualization, S.d., F.I., M.S., M.M. and A.Q.; Methodology, S.d., M.S.,
M.M. and A.Q.; Investigation, S.d., F.I., V.D.M., M.S., M.M. and A.Q.; Writing—original draft prepa-
ration, S.d., M.S., M.M. and A.Q.; Writing—review and editing, S.d., F.I., V.D.M., M.S., M.M. and A.Q.
All authors have read and agreed to the published version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Data Availability Statement: Not applicable.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Casey, R.A.; Loftus, B.; Bolster, C.; Richards, G.J.; Blackwell, E.J. Human directed aggression in domestic dogs (Canis familiaris):
Occurrence in different contexts and risk factors. Appl. Anim. Behav. Sci. 2014,152, 52–63. [CrossRef]
2.
Powell, L.; Stefanovski, D.; Siracusa, C.; Serpell, J. Owner personality, owner-dog attachment, and canine demographics influence
treatment outcomes in canine behavioral medicine cases. Front. Veter. Sci. 2021,7, 1238. [CrossRef]
3.
Polo, G.; Calderón, N.; Clothier, S.; Garcia, R.D.C.M. Understanding dog aggression: Epidemiological aspects: Epidemiologic
aspects: In memoriam, Rudy de Meester (1953–2012). J. Vet. Behav. 2015,10, 525–534. [CrossRef]

Animals 2021,11, 2907 6 of 7
4.
Lockwood, R. Ethology, ecology and epidemiology of canine aggression. In The Domestic Dog: Its Evolution, Behavior & Interactions
with People; Serpell, J., Ed.; Cambridge University Press: Cambridge, UK, 2016; pp. 160–181; ISBN 978-110-769-934-2.
5.
Sacks, J.J.; Sinclair, L.; Gilchrist, J.; Golab, G.C.; Lockwood, R. Breeds of dogs involved in fatal human attacks in the United States
between 1979 and 1998. J. Am. Veter. Med. Assoc. 2000,217, 836–840. [CrossRef] [PubMed]
6.
Sarcey, G.; Ricard, C.; Thelot, B.; Beata, C. Descriptive study of dog bites in France—severity factors, factors of onset of sequelae,
and circumstances. Results of a survey conducted by In VS and Zoopsy in 2009–2010. J. Veter. Behav.
2017
,22, 66–74. [CrossRef]
7.
Ciceroni, C.; Gostinicchi, S. Indagine Epidemiologica Sulle Aggressioni ad Esito Letale in Italia Negli Anni 1984–2009. Le
Point Veterinaire Italie Srl, Edizioni Veterinarie e Agrozootecniche Argomenti N1 2009; Volume 6, p. 67. Available online:
https://sivemp.it/wp/wp-content/uploads/2019/03/21_67_72_aggressivitabis.pdf (accessed on 5 October 2021).
8.
Barrios, C.L.; Bustos-López, C.; Pavletic, C.; Parra, A.; Vidal, M.; Bowen, J.; Fatjó, J. Epidemiology of dog bite incidents in Chile:
Factors related to the patterns of human-dog relationship. Animals 2021,11, 96. [CrossRef]
9.
Farhoody, P.; Mallawaarachchi, I.; Tarwater, P.M.; Serpell, J.A.; Duffy, D.L.; Zink, C. Aggression toward familiar people, strangers,
and conspecifics in gonadectomized and intact dogs. Front. Veter. Sci. 2018,5, 18. [CrossRef]
10.
Reisner, I.R.; Nance, M.L.; Zeller, J.S.; Houseknecht, E.M.; Kassam-Adams, N.; Wiebe, D.J. Behavioral characteristics associated
with dog bites to children presenting to an urban trauma centre. Inj. Prev. 2011,17, 348–353. [CrossRef]
11.
Reisner, I.R.; Shofer, F.S.; Nance, M.L. Behavioral assessment of child-directed canine aggression. Inj. Prev.
2007
,13, 348–351.
[CrossRef]
12.
Guy, N.; Luescher, U.; Dohoo, S.; Spangler, E.; Miller, J.; Dohoo, I.; Bate, L. A case series of biting dogs: Characteristics of the dogs,
their behaviour, and their victims. Appl. Anim. Behav. Sci. 2001,74, 43–57. [CrossRef]
13.
O’Sullivan, E.N.; Jones, B.R.; O’Sullivan, K.; Hanlon, A.J. The management and behavioural history of 100 dogs reported for
biting a person. Appl. Anim. Behav. Sci. 2008,114, 149–158. [CrossRef]
14.
d’Angelo, D.; Ciani, F.; Zaccherini, A.; Tafuri, S.; Avallone, L.; D’Ingeo, S.; Quaranta, A. Human-animal relationship dysfunction:
A case study of animal hoarding in Italy. Animals 2020,10, 1501. [CrossRef] [PubMed]
15.
Siniscalchi, M.; d’Ingeo, S.; Quaranta, A. Lateralized emotional functioning in domestic animals. Appl. Anim. Behav. Sci.
2021
,237,
105282. [CrossRef]
16.
Siniscalchi, M.; d’Ingeo, S.; Quaranta, A. Orienting asymmetries and physiological reactivity in dogs’ response to human
emotional faces. Learn. Behav. 2018,46, 574–585. [CrossRef] [PubMed]
17.
Siniscalchi, M.; d’Ingeo, S.; Fornelli, S.; Quaranta, A. Lateralized behavior and cardiac activity of dogs in response to human
emotional vocalizations. Sci. Rep. 2018,8, 77. [CrossRef] [PubMed]
18.
Siniscalchi, M.; d’Ingeo, S.; Quaranta, A. The dog nose “knows” fear: Asymmetric nostril use during sniffing at canine and
human emotional stimuli. Behav. Brain Res. 2016,304, 34–41. [CrossRef]
19.
Lindsay, S.R. Handbook of Applied Dog Behavior and Training, Adaptation and Learning; John Wiley and Sons: Hoboken, NJ, USA,
2013; ISBN 978-0813807546.
20.
Handelman, B. Canine Behavior: A Photo Illustrated Handbook; Dogwise Publishing: Wenatchee, WA, USA, 2012; ISBN 097-651-182-7.
21. Siniscalchi, M.; d’Ingeo, S.; Minunno, M.; Quaranta, A. Communication in Dogs. Animals 2018,8, 131. [CrossRef]
22.
Weinshenker, N.J.; Siegel, A. Bimodal classification of aggression: Affective defense and predatory attack. Aggress. Violent Behav.
2002,7, 237–250. [CrossRef]
23.
Luescher, A.U.; Reisner, I.R. Canine aggression toward familiar people: A new look at an old problem. Veter. Clin. N. Am. Small
Anim. Pract. 2008,38, 1107–1130. [CrossRef]
24. Chavez, G.A.; Opazo, Á.J. Predatory aggression in a German shepherd dog. J. Veter. Behav. 2012,7, 386–389. [CrossRef]
25.
Schilder, M.B.; van der Borg, J.A.; Vinke, C.M. Intraspecific killing in dogs: Predation behavior or aggression? A study of
aggressors, victims, possible causes, and motivations. J. Veter. Behav. 2019,34, 52–59. [CrossRef]
26.
Haller, J. The role of central and medial amygdala in normal and abnormal aggression: A review of classical approaches. Neurosci.
Biobehav. Rev. 2018,85, 34–43. [CrossRef]
27.
Horwitz, D.; Mills, D. BSAVA Manual of Canine and Feline Behavioural Medicine; British Small Animal Veterinary Association:
Quedgeley, UK, 2009; ISBN 978-190-531-915-2.
28.
Maksymowicz, K.; Marycz, K.; Czogała, J.; Jurek, T. Refutation of the stereotype of a “killer dog” in light of the behavioral
interpretation of human corpses biting by domestic dogs. J. Veter. Behav. 2011,6, 50–56. [CrossRef]
29.
Overall, K.L. Clinical Behavioral Medicine for Small Animals; Mosby Year Book Inc.: St Louis, MI, USA, 1997; ISBN 978-0801668203.
30.
Maksymowicz, K.; Janeczek, A.; Szotek, S.; Łukomski, R.; Dawidowicz, J. Dog bites in humans in a large urban agglomeration in
the southwest of Poland, an analysis of forensic medical records. J. Veter. Behav. 2016,12, 20–26. [CrossRef]
31.
Aloff, B. Aggression in Dogs—Practical Management, Prevention & Behavior Modification; Dogwise Publishing: Wenatchee, DC, USA,
2002; ISBN 978-192-924-220-7.
32.
Panksepp, J. Affective Neuroscience: The Foundations of Human and Animal Emotions; Oxford University Press: Oxford, UK, 2004;
ISBN 978-0195178050.
33.
Holmes, R. What do we know, and what should we know, about the emotional variation of dogs confined to bakyards? In
Proceedings of the Veterinary Behaviour Chapter Scientific Week 2013. Gold Coast, Australia, 11–13 July 2013.
34. Baik, J.-H. Stress and the dopaminergic reward system. Exp. Mol. Med. 2020,52, 1879–1890. [CrossRef] [PubMed]

Animals 2021,11, 2907 7 of 7
35.
Bromberg-Martin, E.S.; Matsumoto, M.; Hikosaka, O. Dopamine in motivational control: Rewarding, aversive, and alerting.
Neuron 2010,68, 815–834. [CrossRef]
36.
Part, C.; Kiddie, J.; Hayes, W.; Mills, D.; Neville, R.; Morton, D.; Collins, L. Physiological, physical and behavioural changes in
dogs (Canis familiaris) when kennelled: Testing the validity of stress parameters. Physiol. Behav. 2014,133, 260–271. [CrossRef]
37. Roberts, M.B.V. Biology: A Functional Approach; Nelson Thornes: Cheltenham, UK, 2014; ISBN 978-017-448-019-8.
38.
Mason, G. Stereotypic behaviour in captive animals: Fundamentals and implications for welfare and beyond. Stereotypic Anim.
Behav. Fundam. Appl. Welf. 2006,2, 325–356. [CrossRef]
39.
McPeake, K.J.; Collins, L.; Zulch, H.; Mills, D.S. The canine frustration questionnaire—development of a new psychometric tool
for measuring frustration in domestic dogs (Canis familiaris). Front. Veter. Sci. 2019,6, 152. [CrossRef]
40.
Coppinger, R.; Coppinger, L. Dogs: A Startling New Understanding of Canine Origin, Behavior & Evolution; Simon and Schuster:
New York, NY, USA, 2001; ISBN 978-068-485-530-1.
41.
Udell, M.A.; Ewald, M.; Dorey, N.R.; Wynne, C.D. Exploring breed differences in dogs (Canis familiaris): Does exaggeration or
inhibition of predatory response predict performance on human-guided tasks? Anim. Behav. 2014,89, 99–105. [CrossRef]
42.
Clark, A.R.; Brace, A.H. The International Encyclopedia of Dogs; Nowell Book House: New York, NY, USA, 1995; ISBN 978-087-605-624-0.
43.
Kemp, T.J.; Bachus, K.N.; Nairn, J.A.; Carrier, D.R. Functional trade-offs in the limb bones of dogs selected for running versus
fighting. J. Exp. Biol. 2005,208, 3475–3482. [CrossRef]
44.
Lockwood, R.; Rindy, K. Are “pit bulls” different? An analysis of the pit bull terrier controversy. Anthrozoös
1987
,1, 2–8.
[CrossRef]
45.
Prendes, M.A.; Jian-Amadi, A.; Chang, S.-H.; Shaftel, S.S. Ocular trauma from dog bites: Characterization, associations, and
treatment patterns at a regional level I trauma center over 11 years. Ophthalmic Plast. Reconstr. Surg.
2016
,32, 279–283. [CrossRef]
[PubMed]
46.
Kasbekar, A.; Garfit, H.; Duncan, C.; Mehta, B.; Davies, K.; Narasimhan, G.; Donne, A. Dog bites to the head and neck in children;
an increasing problem in the UK. Clin. Otolaryngol. 2013,38, 259–262. [CrossRef] [PubMed]
47.
Overall, K.L.; Love, M. Dog bites to humans—demography, epidemiology, injury, and risk. J. Am. Veter. Med. Assoc.
2001
,218,
1923–1934. [CrossRef] [PubMed]
48.
O’Brien, D.C.; Andre, T.B.; Robinson, A.D.; Squires, L.; Tollefson, T.T. Dog bites of the head and neck: An evaluation of a common
pediatric trauma and associated treatment. Am. J. Otolaryngol. 2015,36, 32–38. [CrossRef] [PubMed]
49.
Benevento, M.; Trotta, S.; Iarussi, F.; Caterino, C.; Jarussi, V.; Solarino, B. Multidisciplinary analysis of bite marks in a fatal human
dog attack: A case report. Leg. Med. 2021,48, 101816. [CrossRef] [PubMed]
50.
Reese, L.A.; Vertalka, J.J. Understanding dog bites: The important role of human behavior. J. Appl. Anim. Welf. Sci.
2020
,24, 1–16.
[CrossRef]
51.
Webster, C.A.; Farnworth, M.J. Ability of the public to recognize dogs considered to be dangerous under the dangerous dogs act
in the United Kingdom. J. Appl. Anim. Welf. Sci. 2018,22, 240–254. [CrossRef]
52. Collier, S. Breed-specific legislation and the pit bull terrier: Are the laws justified? J. Veter. Behav. 2006,1, 17–22. [CrossRef]