when pigs fly

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when pigs fly

Never, as in Sure he'll pay for the drinks-when pigs fly. Equating the flight of pigs with something impossible dates from the early 1600s, when several writers alleged that pigs fly with their tails forward. The idiom is also put as pigs may fly.
See also: fly, pig
References in periodicals archive ?
The answer would be for people to stop paying the exorbitant admission prices at the grounds, but then pigs may fly.
PIGS may fly and, under certain high-octane circumstances, cows can no doubt be observed jumping over the moon.