Leonard: Come on, Sheldon. You can't turn your back on physics. Besides, you have no idea what you're doing with this stuff.
Howard: But if you really want to learn the mechanical side, I can teach you anything you want to know.
Leonard: And instead of standing around watching, you can help us build your smaller guidance system.
Howard: And with all these new skills, you'd be able to fix any model train. You'd be the king of the train store!
Sheldon: Excuse me. I have a girlfriend. I'm already king of the train store.