People get tired when they travel. It's a given. All the stress from the airports, hurrying to one's gate, long lines at security, overly sensitive metal detectors which give rise to the need for a full body pat down (yes - a full body pat down by a Frenchman - not my happiest moment).
So its no wonder why people often sleep on the plane. The airport exhausted them. Unfortunately, not all of us can fall asleep on a plane. The cramp, crowded seats... the fact that you can't recline but only a few inches... and all the noise is not conducive to sleep.
It's possible that this lack of sleep allowed the following to occurred between a French speaking flight attendant and somewhat confused American tourist on the flight from Paris to Bucharest:
FFA: (says something obviously in French and therefore unintelligible to the American Tourist)
AT: Excuse Me?
FFA: (Smiling) What would you like to drink?
AT: Water please
FFA: Would like you that with gas?
AT: (Confused look) Uh...what? Gas? What? Why would there be gas in the water?? (probably thinking after time on planes and the airport the AT had enough gas to last for a while)
FFA: Gas...tiny bubbles - like Club Soda
AT: Oh (dawn of realization - carbonated water)
AT: Just regular water please
Obviously the choice of words can make a big difference in a conversation, and when the person doesn't speak English natively, sometimes the words chosen may technically be correct but not the best for the given situation.
The identity of the AT shall remain anonymous, to protect the innocent, the tired, and the confused.