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.
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.