Okay, it wasn’t Tarantino but his Pulp Fiction co-author Roger Avery. And it began as diamonds, but was changed to a McGuffin later.
you keep using that word. I do not think it means what you think it means.
I wish someone would suck my mono. 
you only have one?
If he had two, it’d be a di.
In the last scene of the movie, ‘Ringo’ orders Jules to open up the briefcase at gun-point.
When he does, Ringo says “Is that what I think it is?”.
How would he know what somebody’s soul looks like?
Yeah, just the one, but if I fold it in half, I can come and go!
IIRC, that’s also the reason Les Nessman on WKRP in Cincinnati always had a band-aid on his face or head; Richard Sanders was wearing one over a real cut in the first scene he filmed, and the producers decided Les was exactly the kind of schlump who’d always have minor wounds.
Well, he knows what diamonds, and gold, and other usual items look like, so if he sees something in the case that he doesn’t know what it is, what else could it be?
Because in a universe where one can put a soul in a briefcase, people know what souls look like.
There was a Certificate of Authenticity signed by the Devil in the briefcase as well.
But, was it notarized?
Wasn’t that how Marge saved Homer from Satan/Flanders?
Feet are filthy. I don’t care if my grandmother’s feet smell like pumpkin pie, I ain’t giving her no goddam foot massage.
What if they taste like pumpkin pie? THEN would you do it?