2. Yawning is contagious, but less so in the summer
Image Source: Rob Faulkner
A good trick if you ever think somebody keeps looking at you is to yawn. If they are, they’re likely to yawn as well subconciously due to yawning being contagious.
However, a 2011 study with 80 participants per season showed that yawning in response to photos only happened 24 percent of the time during summer, compared to 45% of the time during winter. Research also suggests that a yawn cannot be completed without closing your eyes.