Who is Banana Car?

As my friend Jenni says, we will never know.  Sam, age two and a half, has learned "Knock, knock" in part.  It is kind of mysterious seeming because I don't know where he picked it up and because of the following:

Sam:  Knock, knock

Mommy:  Who's there?

Sam:  Banana Car

Mommy:  Banana Car, who?

Sam: (Here he says nothing or he proceeds to "Knock, knock" again, but who is there is never someone as interesting sounding as Banana Car).

So who is Banana Car?  Is he made of an actual banana?  Is he peeled or unpeeled?  Green or ripe?  I guess we will never know.