Your arms and legs seem to be just two versions of the same body part. So why do your legs get kneecaps but your arms don't get elbowcaps? There's a good reason. Find out in the video below.
Why Don't We Have Elbowcaps?
Find out what a sesamoid bone is—and why your arms don't have any.
Why Do We Have 10 Digits?
It might come down to simple math.
Why Do We Have Eyebrows?
Scientists aren't totally sure, but they can guess.
Written by Curiosity Staff December 7, 2016
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