Do you remember that scar that spike has over his left eye on his eyebrow? James Marsters who plays Spike got that in a mugging. The writers wrote it into the script. Spike was fighting the slayer in the Boxer Rebellion and she cut him with her sword.

and its later revealed..i think in the comics, that the reason why spike's scar never healed completely is because the slayer's sword was enchanted or something

It was Spike. Angelus killed the vampire hunter Holtz's family.

Shouldn't this be a pop quiz question instead of a poll? We all know the answer.