Barbara 8111, age 12, of Santa Maria, California, for her question:

Why does yawning sometimes make the eyes watery?

You may deny that yawns, sobs and giggles are related to each other. But in one way they are. All of them can cause the eyes to ooze runny liquid. And for the same reason. Crying, laughing and yawning pucker up the face muscles, especially the muscles around the eyes. This squeezes watery liquid from the tear glands, one in the corner of each eye.

The tear glands make this watery liquid to wash and soothe the eyes. But some help is needed to squeeze it out. When the eyelids blink, the muscles squeeze just enough moisture to wash the surface of the eyes. During a good cry, the muscles around the eyes pucker up tighter and rivers of tears are squeezed out. The same thing happens when the face puckers up with laughter. It is, of course, impossible to yawn a good yawn without squeezing the eyes shut. And the squeezing muscles fill the eyes with teary moisture.