Why did Klingons change appearance?

Related questions

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2. What color is Klingon Blood?
3. Why do Klingons look so different?
4. What is the Klingon battle cruiser?
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6. How big is a Klingon Bird of Prey?
7. What started the Dominion War?
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Tags

1. #episode
2. #explanation
3. #mutated
4. #appearance
5. #given
6. #klingon
7. #lived
8. #rightful
9. #kahless
10. #cloned
11. #before
12. #storyline
13. #enterprise
14. #canonical
15. #change
16. #experiment
17. #klingons