First appearance: “Women of the Prehistoric Planet,” ep. 104
This isn’t a riff explanation, but a callback explanation. The riff “hi-keeba!” appears in numerous MST3k episodes, and could conceivably be confusing if you didn’t know where it originally came from.
The phrase originated from this scene in the series’ fourth-ever episode, where the comic-relief character attempts to show his karate moves to his spaceship crewmates. As he shouts the battle cry of “hi-keeba!” he flips over comically onto his back. It’s one of the goofiest moments in the entire series.
Throughout the rest of the series, the guys would often call back to this moment, yelling “hi-keeba!” during any scene involving chases, acrobatics or any scene of fighting. I wouldn’t be surprised if it shows up in more than a dozen episodes, but there’s no complete list that I know of. Since starting this project, I’ve personally observed it in “Mighty Jack,” “The Magic Sword,” “Viking Women and Sea Serpent,” “Fugitive Alien” and “Stranded in Space.”