What is doot-da-doo?

The cardboard roll in the center of toilet paper, paper towels, wrapping paper etc.

Husband- "Don't throw away the doot-da-doo"!
Wife- "What's a doot-da-doo"?
Husband- (places paper towel roll to lips) "DOOT-DA-DOO"!!! (Smiles)

doot-da-doo - meme gif