why is it sometimes when people laugh & the person laughs with them but

[IsabelleShumake]

they have no idea whats so funny? i have it and sometimes when a person laughs i laugh with them.what is that?

 

[Kim]

laughing can be contagious.

 

[BeatrizCastillon]

a) You want to look cool.

b) You think their laugh is funny

 

[WilliamG1]

You want to be part of the crowd.