Added after a particularly poor, old or obscure joke, the ''Boom''''''Boom'' tagline originated in Music Hall, where a bass drum was struck twice to indicate to an audience that the previous line was indeed a joke. Some people claim that laughter tracks on TV shows are intended to accomplish the same aim, whereas others point to research that shows that laughter tracks "work" because laughter is a primarily sociological phenomenon, and not simply because they indicate where the "jokes" were(n't).

[''However, American laughter tracks are sometimes omitted when shows (eg., MASH) are reshown on British television.'']

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Q: what do you get when you throw two elephants off a cliff?

A: BoomBoom 

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see also RimShot

see also Basil Brush: http://www.bbc.co.uk/cult/ilove/tv/basilbrush/intro.shtml