Brandt: Mr. Lebowski is prepared to make a generous offer to you to act as courier, once we get instructions for the money.
The Dude: Why me, man?
Brandt: He believes the culprits might be the very people who, uh, soiled your rug, and you are in a unique position to confirm or disconfirm that suspicion.
The Dude: He thinks the carpet pissers did this?
Brandt: Well Dude, we just don't know.