A yawn is contagious for many people, especially when someone nearby starts yawning too.

The longer version

Yawning seems to be linked to a form of automatic mimicry that humans share with some other social animals. Seeing or hearing someone yawn activates the same motor pattern in the observer, so the response is triggered without any deliberate decision. Regions of the brain involved in imitation and in reading the actions of others appear to take part, though the exact pathway is still debated.

The effect tends to be stronger between people who know each other well, and simply reading about yawning is often enough to set it off. Scientists have proposed explanations ranging from brain cooling to social synchronisation, but no single account has won general agreement. Whatever its original purpose, the contagious version spreads through a group easily.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.