I came across an interesting post about contagious behavior: being sick. The author said that this is a known phenomenon called mass psychogenic illness. This means that symptoms are passed for one person to the next amongst people who are visible to each other. In the article, mass psychogenic illness is an example (extreme example) of contagious behavior-the unconscious communication of actions or emotions from person to the next. Many behaviors are contagious as well, like sleepiness, sadness, etc.