Ever wondered what your pets are dreaming about when they suddenly kick their paws in their sleep?

Maybe they’re chasing a mouse, or a cat. Maybe they’re pawing at you for treats. Or, maybe they’re just running around the house, rummaging through the garbage, scratching the couch, jumping on beds — all the things they’re not allowed to do when they’re awake.

It’s hard to say. But one thing is for sure: People have been connecting these sudden twitches to dreams in animals, and in humans, for years.

In humans, during the deepest stage of sleep, we have twitches in our limbs but also in our eyes. These are called rapid eye movements, REM for short. And, the science here is pretty certain. REM sleep is when we are likely dreaming.

In animals, scientists also believe their twitching limbs is a likely sign of them dreaming as well.

“I mean, we know we have dreams. We know that we are moving around in our dreams to some extent,” says Mark Blumberg, a neuroscientist at the University of Iowa. “So it just makes sense to think, ‘Oh, movements. Why wouldn’t they be connected?’”

But then, he observed twitching in really young animals and asked, “A newborn animal has had very little waking risk experiences. What the hell are they dreaming about?”

If twitching was really related to dreaming, you’d expect that the older you get and the more experiences you have, the more you’d dream, and the more you’d twitch.

So, to get to the bottom of this mystery, Blumberg began experimenting on newborn rats. In a study, he surgically disconnected the part of the brain responsible for creating dreams.

“We found no effect at all on twitches. And so I was like, ‘Okay, what is this about?’” If dreams were responsible for twitching, why did cutting the part of the brain responsible for them have no effect?

Blumberg spoke with Unexplainable host Noam Hassenfeld about how this seemingly small question — why do we twitch in our sleep? — has fundamentally shifted how we understand the relationship between the brain and the body.

Below is an excerpt of their conversation, edited for length and clarity. There’s much more in the full podcast, so listen to Unexplainable wherever you get your podcasts, including Apple Podcasts, Pandora, and Spotify.

All right, Mark, just to make sure before we dive in here, when I think of sleep twitches, I think of those twitches I get, like, right when I’m falling asleep.

Hypnic jerks, yeah.

Is that part of this? Is that different?

It’s a........

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