In general, cats do not hallucinate, however, there are instances when a cat can be very ill and it is possible that they could hallucinate. If a cat has an eye condition such as cataracts or glaucoma, hallucinations are also possible. Cats have amazing eyesight and see things that human eyes cannot. It is often thought that a cat is hallucinating because it sees something that the owner does not. It could be a leaf or piece of debris floating around in the air that we don't see in the dark that has their attention.