Why is yawning contagious?

Related questions

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5. Does moving your face cause wrinkles?
6. Does smiling give you wrinkles?
7. What causes uncontrollable smiling?
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Tags

1. #disorder
2. #somebody
3. #empathy
4. #frequently
5. #related
6. #contagious
7. #lower
8. #higher
9. #someone
10. #levels
11. #yawning
12. #people
13. #mental
14. #would
15. #about
16. #popular
17. #scale
18. #theory
19. #yawns