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Rhoda Penmark is a fictional character in William March's 1954 novel The Bad Seed and the stage play adapted from it by Maxwell Anderson. She was portrayed by Patty McCormack in the 1956 film adaptation and by Carrie Wells in the 1985 made for TV remake where her name was changed from Rhoda, to "Rachel".
Rhoda Penmark is an eight-year-old girl who is charming, polite and intelligent beyond her years. Beneath her lovable facade, however, she is a sociopath who is willing to harm and even kill to get what she wants, when she wants. She is also a precociously talented con artist, adept at wrapping adults around her little finger. Her tricks do not work on other children, who can sense her true nature and avoid her. In the beginning of the novel, she brutally murders a classmate and a groundskeeper who suspects her. It is also revealed that she murdered an elderly neighbor and her pet dog a few years before.
March writes that Rhoda's evil is genetic: her maternal grandmother, "the incomparable Bessie Denker", was an infamous serial killer who also began killing at Rhoda's age. Rhoda's mother, Christine, was adopted at a very young age and so she doesn't remember her real parents.
Character history (novel) 
While at a school picnic, Rhoda mercilessly drowns her classmate, Claude Daigle, who won a special penmanship award that she feels she deserved more. After beating him to death with her tap shoes she retrieves the medal and leaves the dead boy's body in a local lake. While no one suspects Rhoda at first, Christine notices that her daughter seems startlingly indifferent and untroubled by the other child's tragic death. Christine, who has always vaguely sensed something wrong with her daughter, is troubled, but dismisses any possibility that Rhoda was actually involved in the boy's death.
Only two adults see through Rhoda's charm: Leroy, the mean-spirited janitor at the Penmarks' apartment building; and, to a lesser extent, her teacher Miss Fern, who observes that she is a poor loser and rather selfish. Once Rhoda was even expelled from a school for repeatedly being caught lying to teachers and staff, who described her as a "cold self-sufficient child, who plays by her own rules".
Leroy sees Rhoda as a kindred spirit and enjoys teasing her. One day he spies on Rhoda and repeatedly threatens to "tell on her" to upset her. Rhoda says no one would believe him, but begins to make plans to get rid of him just in case.
Christine tries to relieve her fears by talking abstractly about the murder with her adopted father and Mrs. Breedlove, a neighbor who dabbles in psychiatric theories about personality. During the conversation, she recovers a long-repressed memory of her real mother, "the incomparable Bessie Denker", a serial poisoner who died in the electric chair. That night, Claude's mother arrives, distraught and drunk, at Christine's home stating that there is "something funny about this whole thing" and asks Christine to ask Rhoda about her last few moments with the boy. While Christine is locating Rhoda's necklace, which Mrs. Breedlove is having engraved for the child, Christine finds the Penmanship Medal in Rhoda's treasure chest. She confronts Rhoda, who initially denies having done anything wrong, but confesses after Christine finds the bloodied shoes Rhoda had beaten Claude with before drowning him. Christine is horrified, but Rhoda simply cannot understand what all the fuss is about; after all, she says, "it was Claude Daigle who drowned, not me."
While Christine grapples with what to do, Rhoda silences Leroy by setting his mattress on fire while he's sleeping. When she learns what her daughter has done, Christine makes a gut-wrenching decision: she must kill Rhoda to keep her from killing again. She gives her a lethal dose of sleeping pills, hoping she will die without pain, and then commits suicide by shooting herself in the head.
Rhoda survives when a neighbor hears the shot and takes her to the hospital. Nobody is the wiser as to what Rhoda has done, and she is free to kill again.
Patty McCormack portrayed Rhoda in the 1956 film adaptation. The ending was revised to fit the Hays Code, which did not permit characters to get away with their crimes. In this version, Rhoda is killed by a bolt of lightning, while Christine survives her suicide attempt.
She is ranked twelfth on Bloody-Disgusting’s list of "The Top 16 Creepiest Kids in Horror Movie History". Brian Solomon writes, "The grand-mammy of all messed-up horror movie kids, Rhoda Penmark is a pint-sized terror of biblical proportions. If you think the ADHD-addled rugrats you see roaming shopping malls nowadays are bad, you ain’t seen nothin’ yet."