adverb/kɔ.m‿œ̃ pɛ sy.ʁ‿yn twal si.ʁe/
like grease through a goose, as fast as greased lightning (very rapidly)
“René Sussan, Dupont et le bonheur des hommes, 1965, p. 122. Découvert, il fila parmi les gardes ahuris comme un pet sur une toile cirée.” — With his cover blown, he slipped through the dumbstruck guards as fast as greased lightning.
Literally, “like a fart on an oilcloth”.