This chapter illustrates the cognitive abilities of araneophagic jumping spiders. “Portia,” a genus of araneophagic jumping spiders (family Salticidae), appears to have the most versatile and flexible predatory strategy known for an arthropod. A dominant feature of Portia's predatory strategy is aggressive mimicry, a system in which the predator communicates deceitfully with its prey. Typical salticids do not build webs. Instead, they are hunters that catch their prey in stalk-and-leap sequences guided by vision. Salticids differ from all other spiders by having large anteromedial eyes and acute vision. However, the behavior of Portia is anything but typical for a salticid. Besides hunting its prey cursorily, Portia also builds a prey-catching web. The typical prey of a salticid is insects, but Portia's preferred prey is other spiders. Portia frequently hunts web-building spiders from other families by invading their webs and deceiving them with aggressive-mimicry signals. While in the other spider's web, it makes aggressive-mimicry signals by moving legs, palps, abdomen, or some combination of these to make web-borne vibrations. Portia's typical victim, a web-building spider but not a salticid, typically lacks acute vision and instead perceives the world it lives in by interpreting tension and vibration patterns in its web.