Nagel’s famous essay argues that a creature is conscious if there is “something it is like” to be that creature. Bats perceive the world by echolocation, a sense so unlike ours that we cannot imagine its inner feel, however much we learn about their neurons. This, Nagel argues, exposes a gap in purely physical explanations of the mind: science describes from the outside, while consciousness is irreducibly subjective. The paper helped set the stage for what David Chalmers later called the “hard problem” of consciousness. It is also humbling: if we cannot know a bat’s inner world, how well do we know each other’s?