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It's Okay to Be Smart
Why Do We Cry?
Season 6
Episode 20
Why do we cry? It’s weird. Humans leak water out of their faces when they get sad. Are we the only animals that do this? What does it mean? What is it for? Here’s the science of human tears!
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11:30
I went to NASA in Houston to talk to astronaut Don Pettit.
7:20
Why is ice slippery? It's a more complicated answer than it seems!
11:53
Here’s a rundown of a few of the human body’s biggest evolutionary fails!
8:51
Why are trees and other plants green? The answer is full of surprises.
