Penny: This is just to give you ideas. You know, do-do you want something simple and elegant? I mean, do you want a train?
Sheldon: [entering the apartment] Ooh, we're talking about trains.
Amy: Not the kind of trains you like.
Sheldon: Oh, I like all kinds of trains: steam, diesel, coal, elevated, bullet. I defy you to name a train that I don't like.
Penny: The kind on the back of a wedding dress?
Sheldon: I did not see that coming. Good job.