What is the science behind smiling?

Related questions

1. What causes smile lines?
2. Does moving your face cause wrinkles?
3. Is it bad to smile too much?
4. How often should you smile?
5. What can a smile do?
6. What is a real smile called?
7. What do the faces on Snapchat mean?
8. Does smiling make you look older?
9. Does smiling relieve stress?
10. What do the faces mean on SC?

Tags

1. #contract
2. #signal
3. #level
4. #reward
5. #stimulating
6. #hormones
7. #muscles
8. #increasing
9. #processing
10. #emotional
11. #brain
12. #endorphins
13. #happier
14. #further
15. #smile
16. #system
17. #happy
18. #alter
19. #positive
20. #smiling
21. #simple
22. #pathway
23. #thanks
24. #feedback