Expression: Quand on parle du loup (on en voit la queue)
Pronunciation: [ka(n) to(n) parl du loo]
Meaning: Speak of the devil (and he appears)
Literal translation: When you talk about the wolf (you see its tail)
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Notes
The French proverb quand on parle du loup is used just like the English "speak of the devil," when you are talking about someone who arrives right then or shortly after.
It's interesting that in both expressions, the talked-about person is referred to as mean or evil—the devil is worse than a wolf, of course, but the latter is still considered a savage animal. It's also intriguing that in English, the devil appears completely, so to speak, while in French you only see the loup's tail. Somehow the latter seems more ominous as if it's sneaking up on you.
Example
Je pense que Benoît est un vrai... tiens, Benoît ! Quand on parle du loup !
I think Benoît is a real... hey, Benoît! Speak of the devil!