system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is the audio never synched with the actor's mouth in a tv show when the shot is from behind them?
gpt
Because many shows are shot with a single camera. They'll often film the same scene multiple times (from different angles), or at least certain parts. 

They'll then often use some footage from some shots, and then dub audio from other shots over it.

Edit: couple of words, paragraphing.