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!

Originally released by Knowledgemotion, 2018. Streaming video file encoded with permission for digital streaming by Infobase on February 21, 2020.

The Only Animal That Weeps (4:24); .