The Burning

At Camp Blackfoot, several campers pull a prank on the caretaker, "Cropsy". During the night, one camper sneaks into his cabin and sets up a worm-riddled skull next to his bed with candles in the eye sockets. When Cropsy is awoken by the campers banging on his window, he is so frightened by the skull that he knocks it onto his bed, where it ignites his sheets and clothes. Aflame, Cropsy leaps from his bed and knocks over a gas tank, causing flames to spread through the cabin. The boys watch in shock as Cropsy, engulfed in flames, stumbles out and falls into a river. Five years later, Cropsy is released from the hospital, wearing a coat, sunglasses and a hat to hide his deformities. In a fit of rage, he murders a prostitute by repeatedly stabbing her in the chest with a pair of scissors. He then sets out to another summer camp, Camp Stonewater.
Cropsy, now armed with a pair of garden shears, arrives and tries to attack a female camper, Tiger, who is searching for a baseball in the woods, but he hesitates to kill her. The next morning, camper Sally steps out of the shower and is surprised by camper Alfred, who then runs away. Sally's screams bring Karen, Michelle, Todd and Eddy, who catch Alfred. Michelle demands that Alfred leave, but Todd talks to him, learning that Alfred has no friends, and was merely pulling a prank on Sally. Glazer, Sally's boyfriend, later attacks Alfred, but Todd tells Glazer to cool off, and Alfred apologizes to Sally. That night, Alfred spots Cropsy outside his window, but no one believes him.
At the mess hall, Karen tells Michelle that she and Eddy are going to sleep together. The kids all go on a canoe trip up the river. After supper, Karen and Eddy go to a lake to skinny dip. Just as Eddy and Karen are about to have sex, Karen reconsiders, upsetting Eddy. Upon leaving, Karen discovers her clothes strewn about the woods. As she collects them, Cropsy grabs her and slits her throat. The next morning, Michelle finds that Karen has not returned. She and Todd find Eddy, who tells them she left. They discover the canoes have been cut adrift on the lake that surrounds the camp. Michelle does not believe Karen to be the culprit, so some campers go and search far away from the camp. They create a raft to collect the canoes, while other campers and counselors gather wood. Eddy, Fish and Woodstock (Fisher Stevens) board the finished raft along with two female campers, Marnie and Barbara. Alfred begins to explore, while Todd reassures Michelle that Karen is fine. Eddy and the campers spot a canoe and paddle toward it. Woodstock reaches for the canoe only to have Cropsy jump out and savagely kill them all with his shears.
Michelle starts to worry about Karen. As night falls, Glazer finally has sex with Sally, but suffers premature ejaculation. He later goes to get matches to start a fire and resume their intimacy. Cropsy appears behind Sally and forcibly shoves his shears into her chest; she fights to remove the shears but is killed. Alfred finds the spot where the couple are staying, and watches as Glazer returns. He uncovers Sally, but Cropsy is hiding under her body, and stabs his shears through Glazer's neck, pinning him to a tree. Alfred returns to the others. He wakes Todd and tells him about what he just saw. Todd does not believe him until he finds the bodies. He is then attacked by Cropsy, who knocks him out and chases after Alfred. Regaining consciousness, Todd chases after Cropsy with a felling axe. The campers see a raft coming toward them with no one on board moving. When Michelle approaches the raft, she discovers the slaughtered bodies, Woodstock's severed arm falling on her head when she pulls him. She screams in horror while the other campers help her. Todd appears on the nearby island and goes to them, telling the now-terrified campers to evacuate. On the island, she rows the remaining campers - Dave, Tiger, Diane, Sophie, Alan and Rhoda - towards the campsite. Meanwhile, Cropsy has captured Alfred and drags him towards an abandoned mine shaft. Todd follows, eventually tracking down Alfred in the mine, where Cropsy has pinned him to the wall with the shears through his arm.
Michelle returns with the campers and calls the police to helicopter the kids and survivors to safety. Todd looks through the mine opening for Cropsy and Alfred. When he steps across a piece of track, a mine car up on a raft rolls down, causing him to fall. He falls through a wall and discovers Karen's body hanging from the ceiling. He and Cropsy struggle as Cropsy tries to kill Todd with a blowtorch. When Cropsy's hat falls off and Todd sees his disfigurement, he realizes who the killer is, as well as his own role in the tragic prank. Alfred frees himself and helps Todd by stabbing Cropsy in the back with his own shears, seemingly killing him. The police finally arrive, while Michelle travels by boat to find Todd and Alfred. While Todd and Alfred are leaving, Cropsy, not as dead as they thought, rises up and attacks them. Todd finally succeeds in killing Cropsy by slamming his axe into his face, then Alfred ignites his clothes with Cropsy's blowtorch. Afterward, Alfred and Todd make their way out to Michelle, who brings them to the helicopter and then to the hospital, as Cropsy's body continues to burn. The film ends with another group of teenagers telling the story of Cropsy around the campfire.

Question: Why does Glazer leave Sally alone?
Answer: To find matches