This is a belief from the Mediterranean region, and you can even find evidence of it in the Bible. For instance, in Numbers, Chapter 31, we find this injunction:

"19. And do ye abide without the camp seven days: whosoever hath killed any person, and whosoever hath touched any slain, purify both yourselves and your captives on the third day, and on the seventh day.
20. And purify all your raiment, and all that is made of skins, and all work of goats' hair, and all things made of wood."

The "purification" required is because of blood that might have gotten on your clothes, skin, etc. Or at least that's one reading -- I don't want to get into a full scholarly debate here, only explain how it's being used in Thunderstruck.

For those of you who ever played Dungeons & Dragons, this notion of blood pollution may explain a certain rule to you. In the game, the Priest (or Cleric) class has a restriction of only being able to use blunt weaponry. Why is that? It's an artifact of this blood pollution fear -- a holy person doesn't want to risk his sacred energy by getting splattered with blood in battle. Thus, he wields nothing with an edge.

(It's an imperfect solution, I should say. Braining someone with a mace is going to make a mess as bloody as if you hit them with a sword. Nevertheless, I'm pretty sure that's where the idea came from.)

- Grayson Towler
June, 2006