Why are yawns contagious?

Here is something for the five people who had picnic with me that one rainy Saturday afternoon. I apologize for not having a better source than WHY DO MEN HAVE NIPPLES? Hundreds of Questions You'd Only Ask a Doctor After Your Third Martini by Mark Leyner & Billy Goldberg MD.

Anyways, here it goes. Verbatim.

Why are yawns contagious?
Here are several things we can be thankful are not contagious:
drooling
nosebleeding
itching
seizures
farting

That said, there are several theories for what causes yawns and why they are contagious. It was originally thought that people yawned to get more oxygen, but this appears not to be true.

The most common theory is behavioral. Ina an article examining contagious yawns, Dr. Steven M. Platek and others state, "Contagious yawning may be associated with empathic aspects of mental state attribution and are negatively affected by increases in schizotypal personality traits much like other self-processing related tasks."

Huh? I find myself yawning right now.

What they mean is that people are unconsciously imitating others when they yawn. Yawning is seen in many animals, including cats, fish, and birds, although we don't know what a yawning fish looks like either.