The riff: Exlaimed by Joel as a boy with particularly bad posture stands behind a sheet and exposes his S-shaped spine in shadow form to the assembled class.
The explanation: “Pudd’nhead Wilson” was the name of an 1894 novel by Mark Twain, not one of his more remembered works today. It was about young lawyer named David Wilson who moves to a small Missouri frontier town (likely based on the towns of Twain’s youth) and is dubbed “Pudd’nhead” by the townspeople when a remark he makes is misunderstood. If it’s not clear from the context, it’s meant to mean “dumb.” Eventually, Pudd’nhead turns the tables by solving a murder with the help of his odd hobby, which involves collecting people’s fingerprints.
Novelty factor: I must admit I’d never heard of this Twain novel before, although I’ve heard the term “pudd’nhead” to refer to a nitwit.