Researchers believe that yawning is the body physiological way of keeping the brain nice and cool. It was believed that yawning was how the body increased its oxygen intake when someone was sleepy, and to help them wake up.

But this theory sounds way better. The act of yawning increases your heart rate, blood flow, and uses muscles in the face that are all connected to keeping the brain cooled.

Exhaustion and sleep deprivation can contribute to a rise in the brain's temperature, which is why we tend to yawn more often when we're tired.

So how do you explain you yawning when you saw the top image? The phenomenon is believed to be tied to our ability to empathize with others. Try this on kids below the age of five and they won't yawn back with you. The reason? Their empathetic abilities have yet to fully develop.

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