Mick O'Brien (Sean Penn) is a 16-year-old Irish-American hoodlum from Chicago. While most of Mick's crimes involve snatching purses, vandalism, and getting into brawls, he aspires to bigger and meaner things, which leads him to attempt ripping off a Puerto Rican rival, Paco Moreno (Esai Morales). Everything goes wrong: Mick's partner and best friend Carl (Alan Ruck) is killed, and Mick, while trying to escape the police, accidentally runs over and kills an eight-year-old boy who happens to be Paco's brother. Mick is sent to the Rainford Juvenile Correctional Facility rather than a state prison for adults. Most of the wardens and counselors seem to have lowered themselves to the role of zookeepers. The only exception is Ramon Herrera (Reni Santoni), a former gang member who talks tough to the inmates, but holds out hope for some of them, especially Mick.
Mick's cellmate is Barry Horowitz (Eric Gurry), a small, wiry, brainy Jewish kid who firebombed a bowling alley after some boys there severely beat him (for flirting with their girlfriends). Their cell block is dominated by a pair of brawny sadists named "Viking" Lofgren (Clancy Brown) and Warren "Tweety" Jerome (Robert Lee Rush). As soon as their alpha male status is established, Mick takes his first step toward defining himself by refusing to be intimidated by them. Meanwhile, to avenge his brother's death, Paco rapes Mick's girlfriend J.C. (Ally Sheedy). After hearing of the rape, Mick is desperate to see her, so he and Horowitz escape the double perimeter fences during football practice via the use of a corrosive paste placed on the fences, making the fences weak enough to kick open. Mick escapes, but Horowitz falls on barbed wire and is then caught where a counselor beats him up for calling him names and escaping. Ramon believes that Mick had gone to J.C.'s house, and soon picks him up. He then takes him on a trip to a maximum-security prison to show what's in store for him, should he continue down the path of crime.
After Paco's arrest upon the police finding out about the rape on J.C., he is sentenced to the same dormitory at Rainford that Mick is in. The staff are fully aware of this potential danger, but no other reform school has a vacancy. Meanwhile, in an attempt to injure Paco for Mick, Horowitz plants fertilizer into a radio that he has placed in Paco and Viking's cell. When the charge explodes prematurely and only injures Viking, Horowitz is condemned to permanent solitary confinement, a fate he fears more than any other.
Eventually, Paco's transfer is arranged, so he plans his showdown with Mick for the night before. While Herrera was on night patrol, Paco fakes a ruptured appendix so Herrera comes to his aid. Herrera is assaulted, then caged in the office. The door into the cells is then barricaded, and the entire dormitory is aroused by the brawl. Eventually, Mick comes out on top, and the film ends with him very nearly killing Paco while being encouraged by the others to do it. However, resisting at the last second, he doesnÂ´t do it. He then drags a beaten Paco in front of the caged Ramon and other detention officers and heads back to his cell, crying in remorse.

Question: How does Horowitz attempt to injure Paco?
Answer: By planting a bomb in his cell.