If you have ever had a cat or a dog, you have surely seen them move their paws and eyes while sleeping. 

If you see your pet moving while they sleep, don't worry, your pet is dreaming.

Scientists have studied animals in their sleep and their movements and have found that some mammals dream just like us. 

One phase that we have while sleeping is called REM (Rapid Eye Movement), when our eyes move back and forth very fast as we sleep. During REM, we usually dream. 

So, scientists found that dogs and cats also go through REM and so they also dream. Maybe they are processing memories or going over happy moments they had that day?

Also, our pets could even have nightmares. That's what is happening to the pup in the video, which also seems to be crying.