THE SCIENCE OF Itching. “Why is it that watching someone else’s finger being hit with a hammer will usually not make us withdraw our own fingers, but watching someone scratch will make us feel itchy and cause us to scratch as well? The best guess is as follows: Through most of our human history, we have been routinely exposed to disease- and toxin-bearing parasites. In situations where these occur, if you notice that the person next to you is scratching, there is a good reason to believe you are also being exposed to the same dangerous insect, worm, etc., and it’s therefore adaptive for you to feel itchy and scratch in order to reduce your own chance of harm. Pain, in contrast, is weakly social contagious, because the cause of most pain is not generally spread from person to person.”