They Might Be Giants - Letter / Not a Letter lyrics

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 it is, that's not a letter.

That's a letter.

Is that a letter, or what?

That's a letter. Only it's upside down.