When you’re watching a horror film you may feel your palms get sweaty and your heart starts beating more rapidly, but these are just some of the natural reactions that happen to our bodies when we feel scared.

Our bodies have a fight-or-flight reaction to certain situations, this is a survival mechanism, and it happens when we are in real or perceived danger. Different things scare different people, (with cultural influences and personal experiences playing a significant role), and our bodies respond when we see something that we feel poses a threat.

In response to a scary situation, Smithsonian notes that the heart rate and blood pressure will rise, blood flow to the muscles increases (preparing for an escape), pupils dilate, and breathing becomes more rapid. These are the noticeable effects on the body, but the most interesting change is probably not the physical result, but what is happening within the brain.

"The release of neurochemicals and hormones causes an increase in heart rate and breathing, shunts blood away from the intestines and sends more to the muscles, for running or fighting," neuropsychiatrist Dr. Katherine Brownlowe told Live Science. "It puts all the brain's attention into 'fight-or-flight.'"

Business Insider notes that three things tend to happen when we are scared, the first is the freeze action, designed to keep us hidden from a predator, the second is flight, which means we try to escape the perceived threat, and the third is fight, and this happens when it’s no longer possible to remove yourself from danger. According to the publication, the amygdala starts the fear response. What follows, is the release of the brain chemical glutamate to two other areas of the brain, and this often results in our initial “freeze” or jump reaction to fear. The second brain signal is to the hypothalamus, which interprets the threat and the actions that should come next. The publication notes that the hypothalamus is in control of the central nervous system, and this causes our heart rate and blood pressure to rise, as well as a release of adrenaline.

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