While trying to unlock the mystery of the yawn, researchers have determined that when it comes to yawning - size matters.

A new study of YouTube videos featuring 29 different mammals yawning, including people, puppies, kittens and even hedgehogs, revealed the length of the yawn is directly proportional to the size of the brain, and the bigger your brain, the longer your yawn.

The average human yawns for just over six seconds, while a mouse yawn lasts only one and a half seconds.

And for those who think we yawn because we're tired or lazy, researchers say the real reason we yawn is to cool the brain, which can run hot.

Source: ABC News Radio

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