Even when you're not cutting onions or watching Titantic, your eyes are constantly producing tears.

We actually produce three different types of tears: basal, reflex, and emotional. Basal tears and reflex tears are pretty easy to understand: they protect our eyes from debris or wash away potentially harmful substances and microorganisms. However, scientists are only just beginning to deduce why we produce emotional tears – is it to release hormones, or more of a social signal?

This video by TED-Ed gives you the science behind sobbing with an animation of Iris, the iris.