Watch even the most graceful person apply mascara, and nine times out of 10 their mouth will drop open as if you just asked them the square root of Pi. Since the reason why is less universally understood, we asked Blanca Cobb, a body language expert.
"The open mouth phenomenon is a subconscious action," she told POPSUGAR. "You don't realize that you're doing it." Though the contortion might look weird, it actually serves a purpose. Anyone who has ever accidentally shoved a mascara wand to their eyelid knows that's not an optimal outcome, so when we put on mascara, we try to keep our eyes as open and still as possible. "Two different nerves control the muscles that open and close your mouth and upper eyelids, and those nerves are located close together on your body," Cobb said. "The leading theory for why your mouth opens while you apply mascara is because those nerves are cross-firing."
Once you learn how to apply mascara that way, it can be tough to consciously undo the act. "It's reinforced behavior," Cobb said. "You just sense that it works, so you continue to put mascara on that way." The more you know.