Wrong Turn 3: Left for Dead

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Alex (Janet Montgomery) and her friends Trey (Jack Gordon), Sophie (Louise Cliffe) and Brent (Charley Speed) go into the woods of West Virginia on a rafting trip. As they are camping, Alex's friends are killed by Three Finger. Sheriff Carver and Deputy Lane receive a report about the missing group.
Two days later, prison guard Nate (Tom Frederic) is assigned with Walter (Chucky Venn) and Preslow (Mike Straub) to transfer a group of prisoners to a distant prison. The prisoners are Crawford (Jake Curran), a car thief, Floyd (Gil Kolirin), a neo-Nazi serial killer, Brandon (Tom McKay), who was wrongly convicted of murder, Chavez (Tamer Hassan), the leader of a crime organization and Willy (Christian Contreras), an undercover agent who is posing as a prisoner in order to get information from Chavez. While driving, their bus is rammed by Three Finger's truck and crashes in the woods of West Virginia, forcing them to continue on foot. Walter is badly injured, but Nate manages to rescue him from the truck before it explodes.
They begin to follow Alex, and on the way, they find an abandoned armored truck. Chavez tells Nate to check the cab of the truck. Nate finds a set of keys and a gun. He secretly gives the gun to Walter, after handing the keys over to Chavez. Chavez uses the keys to open the back of the truck, and finds several bags of money. He intends to steal the money and demands that everyone carry two bags, but Walter refuses because of his injury. In a last-ditch effort to regain control of the situation, Walter pulls out the gun and tries to shoot Chavez. Unfortunately, the gun is not loaded and Chavez shoots and kills Walter. Chavez forces those left alive to carry the money and they continue on foot.
Along the trail, they stumble upon a trap, set by Three Toes, Three Finger's son. They escape then catch the son and behead him, leaving a trophy on the spent booby trap for Three Finger to find as a deterrent. This enrages Three Finger, who sets traps for the group, killing first Willy and then Crawford.
Meanwhile, Sheriff Carver decides to go looking for Nate, and Deputy Lane sets out look for the missing group of rafters. Sheriff Carver manages to find the group, but is soon killed by Three Finger. Soon after, Chavez and Floyd get into a fist fight while Brandon watches, allowing an opportunity for Nate and Alex to escape. After the fight, Chavez and Brandon leave the knocked out Floyd behind. When they hear Alex and Nate talking, they lay the money down and go to find them, taking them hostage again. They are able to find the location where the watch tower once stood, only to discover it was burned down years ago (in the first film). Meanwhile, Floyd finds the money and attempts to run away with it, but he stumbles on some rocks and cries out. Chavez hears him and finds Floyd, only to see Three Finger lobbing a molotov cocktail at Floyd, killing him and burning all the money. Chavez then decides to give Alex to Three Finger to improve his chances of survival. Three Finger drags Alex into his truck and drives off. He secures Alex at his house and goes back out to hunt the rest of the survivors. Meanwhile, Nate wants to go after Alex, but Chavez threatens to kill him if he does so. Fed up, Brandon knocks Chavez unconscious and lets Nate go. After waking up, Chavez finds Three Finger and fights him, but Three Finger overpowers and kills him.
Alex awakens in Three Finger's house, and sees Deputy Lane die in a razor wire net. Nate finds Three Finger's house and frees Alex, but Three Finger attacks him. Alex saves him by stabbing Three Finger with a large stake. Nate and Alex take his tow truck and drive away, but Three Finger follows them and leaps on top of the truck, causing them to crash the truck into a tree. As the truck catches fire, Brandon appears and pulls Alex out. While Brandon is helping Nate, Three Finger attacks them, but Nate manages to stab him in the head with a meathook, (presumably) finally killing him. Afterwards, a U.S. Marshal team arrives and rescues Nate and Alex.
Sometime later, Nate greedily returns to take the remaining money from the armored truck. Brandon appears and betrays him, shooting him in the back with an arrow. While Brandon is taking the money, an unknown cannibal appears and bludgeons him to death with a crude club, implying that Three Finger is still alive.

Question: What is the bus rammed by?
Answer: Three Finger's truck