Mystery #3Tier 2body / joints
Why does your elbow bend only one way?
Your shoulder can swing your arm in full circles, but your elbow only folds in one direction; try to bend it backwards and it stops dead. Why is one joint so free and the other so one-way?
Your guess
What's your hunch about why the elbow only bends one way when the shoulder moves every way?
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
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