Going with the whole "Robot Theme":
Lisa Simpson: Aunt Selma, this may be presumptuous, but have you ever considered artificial insemination?
Homer: Boy, I don't know. You'd have to be pretty desperate to make it with a robot!
[Marge whispers something in his ear]
Homer: I knew that.
Lisa: Dad, what's a Muppet?
Homer: Well, it's not quite a mop, it's not quite a puppet, but man... [laughs hysterically] So to answer your question, I don't know.
(I will personally never let this thread die.)
KeyserSoze