Why Humans Scream, Make Crazy Faces When Terrified

Whether it's because of an outing to a haunted house or due to watching fright-night flicks that make you leave the lights on for days, fear is a deliciously terrifying emotion. For many of us, a sudden scare leads to a scream — a reaction so normal that we rarely consider its scientific origins. But why exactly do we react to fear with an eyes-wide, jaw-dropped, super-loud vocalization?

Well, there's power in the faces we make. As our hosts Julie Douglas and Robert Lamb explain in the Stuff to Blow Your Mind video above, even if there's nothing scary afoot, simply making a scared face will cause you to be more alert. Your eyes will open wider and move faster, allowing you a wider range of vision and better ability to spot impending danger. You will breathe faster, with your nostrils working off a heightened sense of smell (super-handy in case of zombies). And a scared face can affect your emotions. Actually, many different types of facial expressions can impact your emotions, says psychologist William James. Just like smiling can make you feel happier, making a look of terror can create instant vigilance and a total-body fight-or-flight response.

Despite this universal mask of fear, not everyone's faces have the same muscular ability to make it. The risorius muscle is a muscle that controls expression of extreme fear and is usually located on the sides of the mouth. This muscle only appears in about two-thirds of the population, and even then, it ranges greatly in size from one person to another. Some people have this muscle on both sides of the face, while others only have it on one side. The absence or length of the muscle affects the potent form of nonverbal communication known as a look of terror.

As for the scream itself? The theory is that it functions as an audible defense, much like a vehicle's loud alarm system or a baby's cry — impossible to ignore. Studies show that the more irregular, chaotic and animalistic a scream is, the harder it is for others to ignore it. Perhaps that's why those scary movies and their screaming victims are so spellbinding.