I sometimes travel LAX-CDG on AF, with a friend who likes to buy two coach seats so she has a bit of room. After sitting through three attempts at what AF calls "le contage" (or roughly so), I realised that they were looking for my friend's invisible friend. A quick conference with a crew member revealed that they were about to go back to the gate and make everyone get off the aeroplane because the count was incorrect. She was quite grateful that I'd spoken up, and my friend and I got stellar service for the entire journey.

After that, whenever my friend buys a second seat, we alert the purser as soon as we can.

** Note the use, above, of realised, crew (not FA), aeroplane and journey (Journey, in the US, is most often used in reference to a very bad pop group, rather than to what we call a "trip."). I hope I pass the Brit test.