Why do katanas have a blood groove?

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Tags

1. #blade
2. #weight
3. #tempering
4. #normally
5. #grooves
6. #however
7. #combined
8. #strength
9. #stability
10. #reduce
11. #sacrifices
12. #treatment
13. #sword
14. #katana
15. #wikipedia
16. #blood
17. #according
18. #original
19. #methods
20. #retains