Yawn
The yawn reflex has long been observed to be contagious. In 1508, Erasmus wrote, "One man's yawning makes another yawn.," and the French proverbialized the idea to "Un bon bâilleur en fait bâillier deux." ("One good gaper makes two others gape"). Often, if one person yawns, this may cause another person to "empathetically" yawn. Observing another person's yawning face (especially his/her eyes), even reading, or thinking about yawning, or looking at a yawning picture can cause a person to yawn.