yawn effect 

when someone yawns, then another person yawns, and another, and another, and so on; often occurs in classrooms

I yawned in class. Then Billy yawned, then Kaitlynn, then Alex, then Jill... A perfect example of the yawn effect.

yawn effect by iCoinedThat1199 December 26, 2009

The Yawn Effect 

Effect after one person yawns, similar to the Butterfly Effect.

After I yawned, it seemed as if the entire room was yawning. I had just accidentally started The Yawn Effect.

The Yawn Effect by Yawnnnnnn June 24, 2010