Tamara

Tamara Riley is a shy and unattractive but intelligent girl who likes witchcraft and has a crush on Bill Natolly, her handsome English teacher. When a critical article she writes about the school's athletes is published, two of the star athletes, Shawn and Patrick, want revenge. Tamara attempts to perform a magical ritual to bind her fate to that of her teacher, but when she must spill her own blood she ceases the ritual.That night, a prank is orchestrated by Shawn and Patrick, along with Shawn's girlfriend Kisha. Shawn calls Tamara, impersonating Mr. Natolly, and invites her to a motel room. A video camera is placed there and catches Tamara undressing. Shawn, Patrick, and Kisha watch this, along with three others who did not know about the prank (Chloe, Jesse, and Roger). Shawn comes in and taunts Tamara, and Tamara is accidentally killed in a struggle. Despite Chloe's demands that they inform the police, she is blackmailed into helping bury Tamara.However the very next day, they are shocked when Tamara walks into class, alive and well and looking more attractive than ever before. They convince themselves that she was only unconscious and she dug her way out of the ground. That night, while Roger is watching a movie in the school AV room, the image on the screen suddenly changes to the video of Tamara. Roger removes the tape and is confronted by Tamara. She torments him with hallucinations of what it is like to be buried alive and with his history of cutting himself. The next day, he sends a televised message to the entire school in which he proclaims that one should 'hear no evil, speak no evil, and see no evil.' He then cuts off his ear and tongue with a razor blade, then stabs himself in the eye, which kills him.Tamara then visits the home of Mr. Natolly, intending to seduce him. However, when he resists her, she says that "it is only a matter of time." The next day, she visits the school guidance counselor, Allison Natolly, the wife of Mr. Natolly. Tamara confronts Allison, mentioning Allison and Bill's infertility problems. Realizing that her father fantasizes about being with her and that his alcoholism drove her mother away, Tamara makes her father "finish the bottle", requiring him to eat a beer bottle.At a party, Tamara puts a spell on Patrick and Shawn, and forces them to have sex with each other, with Patrick raping Shawn, just as he has done to girls in the past. Kisha attempts to stop Tamara, but is incapacitated when Tamara begins to talk about Kisha's eating disorder. Tamara tells Kisha that she is "skin and bone, and really should eat more." Kisha begins to eat herself into a stupor, but is taken away by Jesse and Chloe. When Chloe and Jesse call Mr. Natolly and tell him about what happened, Kisha (still under the spell) calls Tamara and tells her that Mr. Natolly knows. Kisha is knocked out by Chloe.Chloe, Jesse, and Mr. Natolly go to Tamara's house, where they find the corpse of Tamara's father and a spellbook describing the ritual Tamara tried to perform. They realize that when they killed Tamara that night, her blood was spilled. It was because of Tamara's blood being spilled that the ritual was completed and allowed her to rise from the grave as what she is.Meanwhile, Tamara, learning of what the others know, sends Shawn and Patrick to the Natolly residence to kill Allison. They try, but Allison kills them both in self-defense after a long and brutal chase and fight. Kisha and Allison are both taken to the hospital and treated, but Kisha wakes up and chases down Jesse and Chloe, resulting in Jesse's death.Tamara then takes control of the mind of an armed security guard and chases Mr. Natolly, Allison, and Chloe up to the rooftop of the hospital. Tamara and Chloe finally confront each other. Tamara is unable to control Chloe because of her being innocent and realizing the monster that she herself has become. She breaks down and slowly changes back into a corpse. Before fading away, Tamara asserts her will to be with Mr. Natolly and he appears to surrender to the inevitable. Mr. Natolly holds Tamara close and kisses her, then throws himself off the roof with Tamara.In the final shot, it is revealed that Chloe and Allison are fine, and Tamara and Mr. Natolly are both dead. However, Kisha, still apparently under the spell, takes the spell book from Chloe's jeep.

Question: What made the spell work?
Answer: Tamara's blood was spilled