system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is it that we laugh more when we watch a movie with others than we do when we watch the movie alone?
gpt
Laughing is primarily a social signal that is used to indicate solidarity with others.  If we are laughing along with other people, it indicates to them that we are similar to them (because the laugh shows that we like the same things).  Robert Provines is a psychologist who has studied laughter and found that people are far more likely to smile or talk when alone than they are to laugh.  The reason laughter is a good social signal is because people can tell when you are faking it (i.e., trying to appear to be a member of the group by pretending you find the same things funny when you really don't), so an honest sounding laugh is a good signal to someone that you like them.