Pop is a sound; the sound a balloon makes when it touches a mohawk, or the sound it makes when you aim a needle at it.
It was also the sound that foreigners made when they came into towns, and that derived from the Pop language.
It was also the sound that that weasel made. He would say, "POP! Goes the weasel" and sometimes countrymen would have had their TVs blown out because of it, too.