Paroles: They Might Be Giants. Here Come The ABCs. Letter/Not a Letter.

What's that?
That is a letter
What is that?
That's not a letter

That's a letter
That's not a letter
That is a letter

Is that a letter?
I don't know what that is
That's so a letter
What is that?

Whatever that is, it's not a letter
That's a letter
Is that a letter, or what?
That's a letter
Only it's upside down