It went ZIP went it moved/And BOP when it stopped/And WHIRR when it stood still./I never knew just what it was/And I guess I never will."" That refrain appears periodically in a tale of a father's childhood toy, which he passes on to his son when the time is right. Some readers will recognize it as the lyrics to Paxton's song of the same name; as a picture-book text, it gallops along, and may have some heads bobbing during the chorus. The toy is truly unfathomable: Sayles gleefully depicts it as a honking, blinking, rolling robot/musical instrument that may have a vacuum cleaner in its ancestry. While her invention can never live up to the imaginary pictures readers will have installed in their minds, it certainly comes close.