What dogs actually dream about and more fun facts about dog dreams, according to pet behavior experts

• Dogs have dreams about normal things from their life — like playtime and baths.
• But dogs can also have nightmares, but you shouldn't wake them even if they seem distressed.

Like humans, dogs make all kinds of small movements and sounds in their sleep. You may see the twitch of a tail or hear your dog whine softly. These are familiar to us as the tell-tale signs of dreaming.

But unlike with humans, you can't simply ask them what kinds of dreams they had when they wake up. Here are some insights from vets about what dogs dream about.

What do dogs dream about?

Like humans, dogs experience rapid eye movement (REM) sleep, which is the deepest phase of sleep where dreaming usually occurs.

"If REM and dreaming 'works' the same way in dogs as in humans, then they probably have dreams about their daily dog experiences," says M. Leanne Lilly, clinical assistant professor and section head of Behavioral Medicine at The Ohio State University College of Veterinary Medicine.

Though there is no way to know for sure what dogs dream about, some small studies and anecdotal accounts give us clues.

In one experiment, researchers temporarily deactivated dogs' pons, the part of the brain that inhibits large muscles from moving during sleep. Under very careful conditions, they were able to observe the sleeping dogs drowsily acting out their dreams.

The researchers speculated that the dogs acted just like they would when active — chasing imaginary birds and behaving normally.

In another account, a man theorized that his dog had just woken up from a dream about bathtime. He knew this because his dog fearfully ran and hid between his legs after waking up, a behavior that only occurs after being bathed.

Do dogs have nightmares?

Dogs can have bad dreams, or dreams generally associated with negative emotions, says Carlo Siracusa, associate professor of clinical behavior medicine at Penn Vet and director of Ryan Hospital's Companion Animal Behavior Medicine.

Twitching eyelids or paws are normal in a sleeping dog, but additional signs might indicate that they're having a nightmare, which include:

• Sweaty paws
• Growling or barking
• Whimpering and whining
• Fast-paced breathing
• Tense jaw

If you think your dog's having a nightmare, don't wake them up because they may react aggressively due to disorientation or fear, Siracusa says.

"Even with humans, we can become combative during that transition from nightmare to wakefulness, and we have a lot more ability to inhibit inappropriate or undesirable behaviors than dogs do," Lilly says. "They are like permanent toddlers in that regard."

Nightmares aren't generally a cause for concern. However, if it seems to be happening a lot more frequently, you might want to take your dog to the vet.

Bad dreams can be associated with sleep disorders, Siracusa says. He strongly recommends discussing any sleep disturbances with the vet, especially if there is aggressive behavior.

Fun facts about dog dreams

Much remains unknown about dogs and how they dream, but here are some interesting facts that dog owners might be interested to know:

• Small dogs dream more frequently than large dogs. Meanwhile, large dogs tend to have fewer but longer dreams.
• Dogs spend about half as much time as people do in the REM stage of sleep where dreaming is thought to occur, Lilly says.
• Puppies dream more than adult dogs, likely because they have plenty of new information to process at night.

Insider's takeaway

We have no way of knowing for certain, but we think dogs dream of the activities they like doing when they're awake.

If you think your dog is having a nightmare based on their body language, don't wake them up because they might react aggressively out of fear or disorientation.