An Ange Passe

The other day while having lunch with some French speakers (in a fancy Chinese/California cusine-y place,) there was a sudden silence as the dozen or so of us stopped chattering. "Ah! Un ange passe," said the facilitator from the Alliance Francaise. The expression was new to me. I can't think of an American equivalent.

I love figures of speech and colloquial expressions. The way one culture sometimes chooses to express something so differently from another. I seldom get to hear or speak French these days.