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View full lesson: http://ed.ted.com/lessons/why-do-we-cry-the-three-types-of-tears-alex-gendler

Whether we cry during a sad movie, while chopping onions, or completely involuntarily, our eyes are constantly producing tears. Alex Gendler tracks a particularly watery day in the life of Iris (the iris) as she cycles through basal, reflex and emotional tears.

Lesson by Alex Gendler, animation by The Moving Company Animation Studio.