The “Nobody claps, one person claps, everyone claps” Phenomenon

Question

What is the word to describe the phenomenon where at first nobody has the intension to clap (after a performance, lecture, etc). But suddenly one person starts clapping loudly, breaking the silence, and there goes the applause! Everyone starts clapping!

Answer 1

Chain reaction (“A series of events, each one causing the next”) is the now-somewhat-cliched term often used for that phenomenon.

Some slightly-less-relevant terms include nucleation, trigger, seed (senses 5 or 6), goad, stimulus, and aforementioned catalysis.