REM = "Rapid Eye Movement". I sometimes drape a hand across the dog's face. It's really obvious when they're dreaming. There's some body twitching. They're dreaming about food, of course.
I have noticed that when they are in a deep sleep they open their eyes and then it takes them a few minutes to get this "what do you want now?!" look on their faces like they are so deep in sleep they are a little unconscience!!! HAHAHAHAH