Here's a really simple, yet really useful word for flight attendants. Airplane engines are loud and it's sometimes hard to hear what passengers are saying. Neighbouring passengers may be sleeping and they may speak quieter so as to not wake their neighbours up. Often when you're asking what someone would like to drink, you're essentially lip-reading their response "coffee" or "water" etc.
Also, especially as a learner of French, it's expected that you won't understand everything a passenger says to you in French, and perhaps getting them to repeat a second time will help your comprehension.
As in English, there are a few ways in French to communicate that you didn't understand or hear, and prompt them to repeat what they just said.
One simple way is to say "Pardon?" (Though written the same in English and in French, note that the pronunciation differs.)
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