This was an argument about the pronunciation of the German word “Zehn” (pronounced [tseːn], for the record)

Inspired by yesterday's Hungarian ty/gy discussion

See also ȵ and ȴ

Some time ago there was a thread something like "what innocent word or phrase in one language can mean something inappropriate in other language?" and today I, when I heard the one-word sentence in the public transport, realized there is one between Czech and English.
It goes like this:
One Czech speaker: (says something)
Another Czech speaker: "fakt?"
In informal Czech you can have one-word sentences, where rest of the words are inferred from context, in this case the word "fakt" means "fact" in English and the sentence is short for "is it (that what you said) a fact?" - native English speaker will probably say "really?" "is it?" "isn't it?" or something like that.
So the frequent phrase which means "really?" can dangerously sound like the past tense of the f-word, unfortunately.