In Pulp Fiction, what's in the briefcase?

It's a homage to a old 50s film-noir that Taratino is a fan of "Kiss Me Deadly" (1955)

It revolves around a box which eveybody is after (and glows when opened) and what's in it is never explained.

http://www.youtube.com/watch?v=3HEJC41P7o8

I've wondered the same thing! I'm probably wrong about this, but I thought maybe it was gold because of the glow it would give off on whoever's face that opened the briefcase.

Marsellus Wallace's soul. The combination of the lock on the briefcase is 666.

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it is a macguffin. that is what hitchcock called it. it means the thing that the characters are after but it doesn't matter what it is. (in the spy movie it is the microfilm. in the heist film it is the money. etc.). tarantino doesn't care, didn't care, what is in the damn briefcase. that is the answer.

They don't say, but if I remember correctly, it's something that glows.

Maybe some crack that vincent got