What triggers a smile?

Related questions

1. What can a smile do?
2. How does Smiling change your brain?
3. Why your smile is beautiful?
4. What does smile mean Snapchat?
5. Does smiling make you look older?
6. Does smiling mean your happy?
7. Can smiling change your mood?
8. What is a smile?
9. How often should you smile?
10. Why is yawning contagious?

Tags

1. #smile
2. #brains
3. #brain
4. #system
5. #increasing
6. #stimulating
7. #transmitted
8. #trigger
9. #muscles
10. #hormones
11. #produced
12. #reward
13. #level
14. #further
15. #happy
16. #contract
17. #endorphins
18. #facial
19. #signal
20. #smiling
21. #signals
22. #neuronal