Watch their eyes - if they look "light" that is their closed eyelid. The snooze, as I call it, minute eyes closed, open look around, close again. For folks with cats as pets, same kind of thing that cats do when they are dozing.
They also close one eye when they want to look at something up-close - monocular vision for close up, binocular for distances. That cute little head tilt isn't actually for looking ahead but rather up with one eye.