Stimpy decides to be an inventor and ends up inventing various devices and gadgets. He has a reluctant Ren try out his Cheese-O-Phone, which allows people to talk to cheese, regardless of their foreign tongues. Next he invents a shaver that allows people to get a close shave without even being there, which leads to him shaving off most of Ren's fur. Before Ren can strangle him, Stimpy presents him with a gift. The gift is Stimpy's latest invention, Stay-Put Socks (socks that never fall down). Ren is at first delighted, but then discovers that the socks are filled with glue. Stimpy departs to get the Stay-Put hat and raincoat, and Ren attempts to go after but can't get out of the socks. When Stimpy returns, he immediately notices that Ren is angry. Therefore, he decides to invent something that will make Ren happy all the time. After a long inventing session, he comes up with the Happy Helmet, a helmet to control Ren's happiness. Ren is thrust into a state of completely forced happiness. He begins doing nice things for Stimpy, such as cleaning out his cat box and ironing his underwear. Then Stimpy brings home a record of his favorite song ("Happy, Happy, Joy Joy" by Stinky Whizzleteats). The two of them begin dancing to the record. In the middle of the dancing, Ren runs into the kitchen and finds a hammer in one of the drawers. He uses the hammer to smash the helmet and then storms back into the living room and begins strangling Stimpy. It is then that he realizes how much he loves being angry and thanks Stimpy for making him enraged. The episode ends with a shot of Ren grinning into the camera while his maniacal laugh plays in the background.
This episode has been considered one of the show's most famous, and also one of the best episodes the show has ever made. It was praised for the song, Happy Happy, Joy Joy!, which was a popular hit from the series since 1992, the year the episode finally came out.
This episode, as well as it's sister episode, Black Hole, are the only two Season 1 episodes that aired in 1992. Every other episode from the first season aired in 1991.
This episode includes the original "Happy, Happy, Joy, Joy" song.
There are cute animals and smiley faces painted above Ren's bed in this episode, due to the influence of the Happy Helmet that forced Ren to be happy.
This is also one of the few episodes where Ren and Stimpy are shown sleeping in seperate beds instead of one.
If it weren't for Stimpy's Invention, the whole series of Ren and Stimpy would have just lasted for only one season. But since it became a huge hit among fans, the show was renewed for a second season.
The current reruns shown on Nicktoons in the UK have cut out the scene where Stimpy displays the "Cheese-O-Phone".
The line "You sick little monkey!" was also used in an episode of South Park.
Due to Ren's creepy smile, this episode was almost never created due to Nick's standards deeming it as an episode that will "terrify children".
The "Ask Dr. Stupid" segment is not available on Nick.