Speak of the devil是在18世纪初开始流行的

Speak of the devil是在18世纪初开始流行的。当时有一种迷信的说法，也就是：speak of the devil and he's sure to appear。如果你说到魔鬼，魔鬼就一定会现身。对，后来就简化成：speak of the devil。

The phrase is an abbreviation of an English proverb. Deriving from the Middle Ages, this proverb was a superstitious prohibition against speaking directly of the devil or of evil in general, which was considered to incite 煽动刺激that party to appear, generally with unfortunate consequences.

during the 19th century it became a warning against eavesdroppers,窃听偷听者and by the 20th century had taken on its present meaning.