In Tasos Frantzolas' talk on sound design, he reveals a traditional trick of the cinematic trade that is likely to surprise most listeners despite its total ubiquity. Other than the voices of actors themselves (and even, to an extent, with those voices) every sound that a spectator hears in a film or TV show is emitted from a different source.
Part of the reason for this filmic mendacity is that it's easier, cheaper, and safer to record fake sounds and pass them off as real (when recording the sound of a punch, for example, it would probably be downright illegal to actually punch someone over and over.) Another reason, though, is that these fake sounds can seem more realistic than the actual noise. Frantzolas shows a short clip of a burning cigarette as one example. While actual burning cigarettes are incredibly quiet, playing video of one while playing the audio of a squished ball of saran wrap tricks listeners' brains into believing the shot.