What do dogs dream?

Sasha has two donut beds. During the day she sleeps in her bed downstairs in the dining room and at night she sleeps in her donut bed in our room.

Sasha doesn't bark much. The last time I heard her bark was a few months back, at a squirrel outside the window in the garden.

Sometimes I watch her when she sleeps, her nose twitches and sometimes there is a muffled series of barking coming out through her throat. It's so cute I cannot tell you in words.

I always wonder what she's dreaming of. Chasing after a cat? A squirrel? A ball? Or ...?