The episode: “Rocketship X-M,” ep. 201
The riff: Said gravely by Joel as a doctor takes a man’s blood pressure.
The explanation: This seems to be a line by Groucho Marx in the 1931 film “Monkey Business,” the third Marx Brothers movie. I’m not sure of the context, because I can’t find an exact clip that contains the line. In the film, the Marx brothers are stowaways on an ocean liner and get press-ganged into service as thugs for a pair of feuding gangsters.
Novelty factor: It does sound like a Groucho line now that I look at it, but I certainly wasn’t recognizing it right of the bat.
NOTE: Since I couldn’t find a clip, here’s a band that stole the phrase for a song title.