Physics
Why does crying make your nose run?
Quick fact
Tears drain from the eyes through the nasolacrimal ducts, which empty into the nasal cavity, mixing with nasal mucus and causing the nose to run.
Why this is interesting
Your nose doesn't produce extra fluid when you cry—it's actually your tears draining down a tiny duct in your eye corner, and they mix with mucus in your nasal cavity, creating that familiar runny nose.