What is the difference between humans and other animals? Many have offered answers to this question. Aristotle thinks the answer is that we are rational.1 Descartes is more extreme, claiming that while substance dualism is true of humans, non-human animals are simply machines, incapable of thoughts.2 Hobbes attributes more sophistication to animals than this, but emphasizes that they lack language.3 Locke emphasizes instead that they lack the power of abstraction.4 It is not just philosophers who make such claims