Why does my nose go runny when I cry?

When you make tears which come from the lacrimal gland in the eye, they run through a tiny duct into the eye. They then run across the eye to the middle of the lower eyelid where there is a little hole called the puncton through which they drain into your nose. So when you cry you make an excess of tears so there is more to drain into your nose making your snot more liquid and your nose runs.