Sheldon: Wait, hold on, hold on. How do we know that you're not gonna take the money and drive away?
Leonard: What ya doing, Skippy?
Sheldon: Exactly what 1970s television crime dramas have taught us.
You give us the helium first.
Dealer: Oh, how do I know you're not gonna drive away without paying me?
Sheldon: Guess I'm not the only one who watches '70s television crime dramas.