Why is it that if a person smiles, people automatically smile back (even if the smile isn't 'for them')??

Question

I have noticed that if I listen to jokes on my ipod, I smile/laugh...and. If I walk in the street, smiling about something, people smile back or say hello. I was thinking of a joke to tell my cousin whilst walking. I grinned, looked ahead...and a woman I've never seen before smiled and said "hiya!"

I think this is part of the 'greet every person like they are a good friend you haven't seen in a long time." - type thing.

Answer 1

Maybe they like smiling and they are smiling at both of them....