Laughter can certainly be a good mood-lifter. I can be having a terrible day, maybe work is getting me down, and someone will start laughing about something. Could be anything, maybe someone told a joke. That will at least get me smiling.

Then they'll be cheerful and maybe say something funny, and within seconds i'll be laughing with them. That's me set for the day, i may still be tired or fed up, but all my worries will have been pushed to the back of my mind and i'll have a genuine smile for the rest of the day. I've found that just a smile can be very contagious, so when you work in a shop like i do, serving customers, it's nice to see them smiling just because you are. =D