With Halloween just a few days away, millions are flocking to horror films and haunted houses for their annual dose of terror. Our latest video uncovers the chemistry behind the spine-tingling sense of fear.

"Fear is the expectation or the anticipation of possible harm... We know that the body is highly sensitive to the possibility of threat, so there are multiple pathways that bring that fear information into the brain," explains Abigail Marsh, Ph.D., associate professor of psychology at Georgetown University. Marsh's research focuses on the neuroscience of fear and empathy in psychopaths, among other topics. In the video, she highlights the key brain chemicals and hormones involved in fear and the accompanying fight or flight response.