When women (or men! 2016 baby!) apply mascara, their mouths often open automatically. It's like a dopier version of the surprise emoji, but sometimes women don't even realize they're doing it. So—because this is the Internet, where every question must have an answer—Mental Floss asked neuroscientist Zeeshan Ozair why people make that face.
The answer: it's the fault of nerves that happen to be close together.
“The trigeminal nerve controls the movement of muscles of mastication, which open and close your jaw,” Ozair tells mental_floss. “Two other nerves, the facial nerve and the oculomotor nerve, together control the movement of eyeballs and eyelids.” Those three nerves all originate in close proximity to one another in the brainstem at a point of origin called a nucleus.
Mascara face may be a kind of physiological fluke. “In several people, connections”—called collaterals—“develop between these different brainstem nuclei,” says Ozair, who’s currently studying human-specific aspects of neural development and corticogenesis (cortical development). “As a consequence of these collaterals, when one nerve is activated, the other is as well.”
If you try, though, you don't have to make that face while applying mascara. It can be overridden, like how you can override the instinct that tells you to inhale and hold your breath instead, or the instinct that tells you not to click on a blog post about the Kardashians even though Kim is doing something real weird.