An unsolved mystery of science

As the saying goes: “The yawn does not mean to lie: either that he is sleepy or that he would like to sleep, or that he has something he cannot say.”

The average daily frequency is 7-8 times and lasts from 3 to 10 seconds.

What causes it?

Undoubtedly, sleep, but it could also be caused by hunger and / or boredom.

However, yawning remains, today, one of the unsolved mysteries of science.