If you’re a pet owner, you’ve probably already guessed that the answer to this is YES! But are they really dreaming – and if so, what in the world do they dream about?

Many scientists say there is evidence to support the notion that dogs, cats, and in fact, every mammal that’s been studied, does experience dreams.

There are two main types of sleep: rapid eye movement (REM) sleep and slow wave sleep (SWS). SWS and REM sleep in pets are very similar to that of humans. During this time, the brain processes information learned during the day. Think of it as sorting new information into different mental file folders.

At some point during these two kinds of sleep, dreams take over — in humans as well as in pets. Thus, the twitching, tail wagging, yipping, and pawing your dog does in his sleep, or the tail whipping, chattering, yowling and swatting from your napping cat is likely a reliving of whatever experiences he’s had while awake.

Of course, human dreams also get a lot of their material from the imagination, which makes us wonder if dogs and cats have imaginations in addition to memories! (Anyone who has witnessed their playful cat pay attention to something that’s seemingly not there, and then react to it, is likely to believe their cat must have an active imagination!) Ever heard a dog dreaming? Listen >

In humans, scientists have found that when awakened during REM sleep, the subject has reported having a dream. During the REM sleep, the human brain has a lot of “gamma activity” going on, just like it does when the person is awake. This means that essentially, the brain is behaving just as it does when conscious. Since every mammal studied shows the same brain activity during REM sleep as us humans, it’s not such a leap to believe that your pet really is dreaming.

Ok – not every mammal studied has the same brain activity. The duck-billed platypus experiences more REM sleep than any other mammal, yet its brain activity is completely different during this time of sleep. However, this should come as no surprise from a mammal that lays eggs.

Adult dogs spend about 10 to 12 percent of their sleeping time in REM sleep. Puppies and kittens spend a much greater proportion of their sleep time in REM sleep, which makes sense since they’ve been so busy all day exploring their new world. They have tons of new data to process, sort and store into their memories.

So the next time your pet has an unusually exciting experience during the morning, pay special attention to his behavior while he naps that afternoon. You might just catch your pet reliving the past — in dreams!