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  It is Labor Day weekend, 1946. Young, virginal Ida Parsons innocuously plays as her father hosts a raucous party. Amid the festivities, an older, drunken man named Tom Rice staggers outside and propositions Ida. When she refuses, he chases her into the woods and brutally rapes her; her dogs break out of their pen and they attack and fatally maul Ida's rapist.
  After the credits, the movie picks up in 1982. Preppy brothers Eric and Nick are borrowing their father's yacht to take their girlfriends, Sandy and Donna, on a weekend outing along with their sister, Carla. At the outset of the trip, Nick demonstrates his intent to be the "alpha male" of the trip, insisting that he be the one to pilot the yacht and at one point pulling a gun on Eric to demonstrate his authority. As the tensions rise between Nick and Eric, Donna and Sandy engage in girl-talk, and geeky Carla silently laments that she is the sole member of the cruise who came along without a significant other.
  That night, fog settles in; Eric and Nick, hearing cries out on the water, discover and rescue a shipwrecked fisherman named Bert. Bert informs them that he wrecked offshore Dog Island, the home of lumber baroness Ida Parsons, who has used her family fortune to hole herself up on the island for the past thirty-five years; now she only makes two annual voyages onto the mainland for necessary supplies, and has never spoken to anyone during these trips. Recovering from the onset of hypothermia, Bert tells the quintet a campfire story about the savagery of the wild dogs which roam Ida's island, acting as her sentries. The story, coupled with the cries of wild animals coming from the nearby island, startle Nick enough that he runs on top of the yacht and tries to speed back to the mainland; instead, he wrecks it, damaging the fuel line and causing it to explode.
  Donna, Eric, Sandy, Nick, and Bert wash up on Dog Island; Bert has been seriously wounded, and Carla is nowhere to be found. Seeking to reclaim his macho status, Nick wanders off into the woods, and is subsequently killed by a hulking figure that breaks down the shed where Nick hides. The next morning, Sandy and Eric go off onto the island, hoping that Ida Parsons will help them get back to the mainland. Shortly after they leave the beach, Bert goes into shock, and Donna desperately tries to warm him by stripping to the waist and lying topless across his shirtless torso; seconds later, the same figure which killed Nick sneaks up behind Donna and Bert, fatally hurling Donna against a rock wall and decapitating Bert.
  At the center of the island, Sandy and Eric discover Ida's fortified cabin, as well as the fact that all of Ida's dogs have died long ago, their mutilated skeletons lying in their pens. In Ida's boathouse, the duo discover Carla alive hiding under a tarp; she apparently washed up at another point on the beach and made it to the compound in the middle of the night.
  In the course of exploring Ida's compound, Eric, Sandy and Carla discover a dust-covered nursery full of antique toys, and a cobweb-covered crib; they also discover Ida Parson's diary, which contains insane, rambling passages about giving birth to a sick child, which she intends to keep sinless by secluding him from all the evils of the outside world. They figure something traumatic must've happened to Ida to cause her to write such things, and reach the conclusion that Ida's son has died, causing her to become delusional. As they continue exploring the house, Sandy comes across Ida's skeletal corpse, positioned in repose in her bedroom. The kids listen to something growling in the basement and become frightened, and decide to collect supplies and head back to the shore to collect the rest of their party so they can formulate an escape from the island in Ida's old rowboat. Even so, they go in the basement to see what they can use. But then they find the dead bodies of Nick and Donna, panic and run away back to the beach.
  Eric and Sandy decide that the one who did it must be Ida Parson's son, left insane by his life of solitude under the care of the imbalanced Ida; with nothing to do but learn from Ida and explore the wilderness, he's become immensely strong, a capable tracker and hunter, and is thoroughly convinced that all outsiders are a threat to him and his mother. With the death of Ida, he was left without any basis for reality, and ended up eating the dogs to surviveâand has now turned to people.
  Eric and Sandy go back to the house and get the matches that Sandy dropped earlier. Ida's son attacks, breaking down the door. Eric attempts to fight using a broken branch, but the mutant grapples with him and fatally breaks Eric's back; once it has killed Eric, it turns it attention to Sandy and chases her upstairs into his mother's bedroom, where Sandy wraps a blanket around her head and, playing Ida, convinces the mutant to leave his mother's bedroom. But when Sandy leaves the room, the mutant is there and pursues Sandy out of the house and to the boathouse. Sandy runs headlong into Carla at the boathouse and the mutant, close behind, grabs Carla and crushes her face and kills her. Sandy manages to lure the man into Ida's boathouse, which she sets on fire; Ida's son is mortally burned in the blaze, but still manages to leap from the water and attack Sandy, chasing her up a hill where she yanks a sharp signpost from the ground and impales the mutant with it. As he dies, we finally see his burned and deformed face.
  Traumatized by the death of her friends and the murder she has been forced to commit, Sandy sits alone on Ida's dock, strongly resembling a scarred and traumatized Ida.
question: What did she hit him on the head with?
answer: signpost