Bentley sleeps with his eyes open

Much as I love cats, there is something primitive, almost reptilian about their eyes. When Bentley is at a certain stage of sleep, his eyes are slits with the pupils rolled down (not up), with a glazed look. Sometimes his eyes are wide open like that. It's disturbing. I think predators have to be ready every second for the next kill, and thus don't even have to open their eyes to wake up.