Dark Blood 
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Boy: He died in a mental institution. Melancholia, so I'm told.
Buffy: Your great, great grandfather? So that makes you...?
Boy: One eighth Hopi and prone to depression. (pause) Dark blood in my veins. Got some dark blood yourself. You're familiar with... the dark side of things.
Boy: It's getting... dark... in here.
Boy: Show me a sane man and I'll show you a real moron.