Also in this week's column:

• Why do some people have three nipples?
• Is it true that a woman's breasts can grow enormously overnight?
• Why is it absolutely impossible to sneeze with your eyes open?

Why do we open our mouths to yawn properly?

Asked by Jeff Grisham of San Antonio, Texas

The involuntary act of yawning usually includes opening the mouth very wide while slowly taking in a deep breath. This contortion of the mouth puts pressure on the salivary glands causing the eyes to sometimes tear-up, causes the throat to better open, and tightens the muscles around the mouth making sure the yawn is better accomplished.

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au