The gang have just explained how they poisoned their rivals in a flip-cup contest years before.
Mac: He doesn't have any poison.
Charlie: I don’t have any on me, but I do keep some in my fridge at home in the relish jar.
Frank: There’s poison in that jar? I thought I was allergic to pickles. What’s in the jar with the skull and crossbones?
Charlie: Well, that’s mayonnaise. It’s a decoy.
Frank: And the mayo?
Charlie: That’s shampoo.
Frank: You're telling I’ve been putting shampoo on my sandwiches?
Charlie: If you’ve been using the mayonnaise, then yeah, probably.