"Replaceable You" is the fourth episode of the twenty-third season of The Simpsons. Jane Lynch guest-starred. It originally aired on November 6, 2011.
Bart's science fair project, a mechanical baby seal, outshines Lisa's brainy asteroid model and quickly becomes a popular pet among the retirement home patrons. Meanwhile, Homer's new and eager assistant, Roz Davis (guest voice Jane Lynch), steals Homer's job, forcing him to team up with Flanders to reveal her true colors and evil past.
At home, Bart is watching an episode of The Itchy & Scratchy Show. After, Lisa shows Bart her science fair project, the prediction that an asteroid would wipe Springfield out in years time. After Bart tells Lisa about his project (a fisteroid hitting Planet Nerd) and Lisa mocks it, Bart looks into another project. He starts to make a cootie shot, similar to his cootie patch from last year. Milhouse asks Bart for a cootie shot as he had touched tongues with his dog, which Bart says is for a fifth time. After Lisa tells him that it is too similar to last year's project, Bart tries to think of a new idea then sees Martin Prince, Jr. hanging outside on a tree by his underwear. Bart then uses his slingshot to get Martin down and asks him to help him with the science fair. In return, Bart would pick him first when playing Basketball. Martin agrees to these terms. Meanwhile, Milhouse and his dog, Puppy Goo-Goo, touch tongues again.
At the Springfield Nuclear Power Plant, Homer is reading a book about nuclear safety until he gets bored and goes to sleep. A woman called Roz Davis comes along and tells Homer that she is his new assistant, much to Homer's pleasure. Homer shows Roz around the plant and tells Roz that she should flatter Mr. Burns to make him happy. Roz then proceeds to flatter Homer as well.
Back at the Simpson home, Bart and Martin are trying to come up with ideas for a project. Bart comes up with the Homer Humiliator, a machine that humiliates Homer. Martin fails to see the scientific value of this project and tells Bart to come up with another project. After seeing Santa's Little Helper wearing a Darth Vader mask, Bart comes up with the Robopet, a robotic pet. Martin thinks this is an excellent idea and they start to make it. Martin is just putting the finishing touches to the baby seal-like toy and turns it on. It then attacks Bart and Martin realizes he got a wire crossed over wrongly. After correcting this, Homer comes into the room and Bart changes the wire back to attack Homer with it.
At the science fair, Bart and Martin present their project with many people thinking it is cute. Seymour Skinner then announces the winner, Bart and Martin with their Robopet, beating Lisa's gloomy project, much to Lisa's annoyance. At the Springfield Retirement Castle, the Robopet goes up to Jasper Beardly and cheers him up after he had been depressed for a long time. Lisa is shocked that something Bart made has changed someone's life. Bart had also managed to get funding for his Homer Humiliator by this time.
Back at the Nuclear Power Plant, Homer gets a call from Barney (on the emergency telephone) asking him to come and see Paul Flart: Water Park Cop with him. Homer agrees and asks Roz to cover for him, which she agrees to. Homer gets home to find Mr. Burns there and he demotes Homer for skipping work as Roz had snitched on him.
At Springfield Elementary School again, Martin and Milhouse fight over who is Bart's best friend. Then, Abraham Simpson and the Old Jewish Man come along and ask Bart for more Robopets. Meanwhile, Homer is in Moe's Tavern then Roz comes in and wins over Lenny and Carl.
In the Retirement Castle again, every resident has a Robopet now and all are happy. Meanwhile, funeral directors are watching through a camera and dislike this new found happiness because it means they have less of a chance of dying. They then reprogram the Robopets to make them kill the old people. Back at the Power Plant, Homer is being humiliated by Roz and really hates his new job as her assistant.
At the Retirement Castle again, Kent Brockman is reporting a story that long time resident Alice Glick has been killed by a Robopet. All the toys are taken into custody as a result. Bart and Martin then go to see Professor Frink to ask him to help reprogram the Robopets and break them out of jail. Frink agrees to this, turning down his date with Miss Wyoming, a super model.
Outside their homes, Homer and Ned discuss Roz and Homer finds out that she doesn't like to be touched. Armed with this information, Homer gets a plan. Enlisting the help of Doug, Gary and Benjamin, they manage this task and break the Robopets out of jail and start them on the way back to the Retirement Castle.
At the Nuclear Power Plant, they are holding an "Employee of the Millennium" awards and Roz wins the prize. No one claps, except Homer, doing so sarcastically. Homer then tells Mr. Burns to hug her as well. When he does this, she attacks Burns, resulting in her getting fired. Roz then tries to explain to Homer that he is smarter than she thought, although Homer fails to understand this.
Eventually, the nerds get the Robopets back to the Retirement Castle and the residents thank Bart and Martin. They then start dancing, as do the funeral directors and in Heaven, Jesus and Alice Glick also start dancing.
Music composing for this episode began around October 17, 2011, recording for the episode began on October 24, 2011, and dubbing began on October 25, 2011. Jane Lynch guest starred as Roz and she recorded her scenes together with Dan Castellaneta.
"Replaceable You" was watched by approximately 7.97 million viewers on the first day. The episode has received mainly mixed views from critics.