The laughing domino effect

The phenomenon in which when one person in a group commences laughing, the rest will follow. The laughter genuine, and can often last for two to three minutes. Usually, this group is often a)high b)idiots c)have been previously laughing at something else, and is thus easy for the laughter to recommence.

Person A laughs. Person B, C, D, E, and F also laughs. This is the laughing domino effect.