The episode: “Stranded in Space,” ep. 305
The riff: Robotically delivered by Tom while he is programmed to be a shooting gallery target for Joel.
The explanation: This is a reference to the tagline for the 1980 sci-fi movie “Saturn 3,” which quite clearly stressed this particular pronunciation in print–all the ads say “Some THING is wrong on Saturn 3.” The movie, which starred Kirk Douglas and Farrah Fawcett, was about a pair of scientists in a small base on one of Saturn’s moons being menaced by a malevolent robot. It was critically panned as derivative and not living up to the FX standard set by “Star Wars” three years earlier. As for why Tom says the line, I think he’s just spouting a threatening-sounding catchphrase to get Joel to shoot. Right before it, Crow spouts an even more obscure riff: “Stop talking and start chalking,” which is apparently from a pool-themed pinball machine.
Novelty factor: I’ve never heard of the movie, but I’m fairly certain this phrase is used several other times throughout the history of MST3k. I seem to remember it being used multiple times in other space-themed movies, and I’ve always wondered at what it meant. I must say, it looks pretty bleak. It seems like there was a dearth of good, original sci-fi in the post-Star Wars period. Nevertheless, the entire film is on YouTube, if you’re curious.