Leonard: Who is it?
Amy: Amy Farrah Fowler.
Sheldon: Darn, she found me.
Leonard: She's been here before.
Sheldon: The only flaw in an otherwise perfect plan. Now get my back, Jack.
Leonard: What do you want me to do?
Sheldon: Tell her I'm not here.
Leonard: Where are you?
Sheldon: I don't know. You'll have to devise a scenario that plausibly explains my absence keeping in mind that the key to a good lie lies in the details.
*Later, Leonard answers the door to Amy*
Leonard: Hi, Amy. Sheldon's not here.
Amy: All right.
Sheldon (to Leonard): Way to go on the details.