Tear
The fluid secreted by the lacrimal glands that moistens and protects the surface of the eye, and that also flows during strong emotion.
Aboard the International Space Station, tears don't stream down a face. In microgravity, surface tension makes them cling around the eye as a growing blob, blocking vision and causing pain if unwiped. Astronaut Chris Hadfield demonstrated it on the ISS in 2013.
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