Why do tears come to my eyes when I yawn?

When people yawn, they tend to tightly shut their eyes, and this does two things. First, it squeezes the lacrimal duct, causing more tears to flow into the eye. Secondly, it squashes closed the tear ducts that drain the tear film from the surface of the eye. As a result, there are more tears in the eye and nowhere for them to go. So, when your yawn ends and you open your eyes again, they are watery...