old slang trivia

[freeneasy]

when we were kids and we'd be walking along and suddenly you'd pick up the strong scent of a dead rat or youd catch the scent of skunk spray or you stepped in a creammy pile of doggie diearrea hidden in plain sight or you managed to trip yourself and fall, like i did, into the freshly opend sewer pit full of all kinds of sewer manuer that the plumber just dug up in your backyard, the first statement out of everybodies mouth would always be "pu, do you stink" or "pu does that ever stink".
what did "pu" stand for?:D