The episode: “The Robot vs. The Aztec Mummy,” ep. 102
The riff: Mumbled by all three of the SOL crew after a character says “Stay quiet, I don’t want you to make the slightest noise.”
The explanation: “Peas and carrots” is a phrase that is often used by extras in the background of a movie or TV scene to mumble to make their lips look like they’re moving in simulated conversation. It’s one of several similar phrases like “watermelon canteloupe” and “natter natter, grommish grommish.” These extras are not micced, and typically “random crowd sound” is piped into the film’s final soundtrack to go with their moving lips. This type of noise is known as “walla,” or “rhubarb” in the U.K., and is recorded by groups of actors.
Novelty factor: I had heard something very similar to this before, but I’m always interested in these behind-the-scenes tidbits. Check out this very boring clip of “walla” in action.