If you've ever attempted to read a book during a roadtrip, you'll know the feeling - that sudden wave of nausea that threatens to get worse unless you look away from the pages and look out the window instead.
According to neuroscientist Dean Burnett, it's our brains telling us we're being poisoned.
Technically speaking it shouldn't cause us any problems, but reading while moving triggers sensory confusion in our brains.
The thalmus, which holds all our sensory information is responsible for sending signals to various parts of the brain. When we're walking, the thalmus tells us to move our legs forward, but when we're reading in a moving car, signals get muddled.
"When we're in a vehicle like a car or a train or a ship especially, you're not actually physically moving," Burnett told NPR. "Your body is still. You've got no signals from the muscles saying 'we are moving right now'.
"But the fluids in your ears obey the laws of physics. And they are sort of rocking around and sloshing because you are actually moving. So what's happening there is the brain's getting mixed messages," he said.
"It's getting signals from the muscles and the eyes saying we are still and signals from the balance sensors saying we're in motion."
Because of how we've evolved as a species, our brains think the only thing that can cause such a sensory mismatch is a poison. So the body tries to get rid of the perceived poison by making you throw up.
And although it's inconvenient, it's just one of the quirks of being human, and there's nothing we can do about it except put the book down.