Li'l bit of background on the twins. Hyphen marks are supposed to be astericks, but FF won't let me do them.
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((Knives and Vash as children:))
Knives: You wanted to save the butterfly, right?
Vash: I wanted to save them both!
Knives: -puzzled- But...you're...arachniphobic...
Vash: What?
Knives: -exasperated- You know, afraid of spiders!
Vash: Yeah, well... still, that doesn't matter! You didn't have to kill the spider!
Knives: -evil grin- Does it really make you that mad?
Vash: YES! You killed it!
Knives: Fine, then...-drops spider on Vash's head- I didn't kill it.
Vash: GAAAAAAAAAAAAAAAAAAAAHH! -runs around in circles while smacking at his head-
Knives: You know, Vash, you scream like a little girl. -calmly walks away-