Urban Legends: Bloody Mary

On November 5, 1969, three high school football players try to drug and kidnap their prom night dates. Their plan works with two of the girls but the third, Mary Banner (Lillith Fields), tries to escape. The football captain chases her into a storage room and punches her, knocking her out. He panics and locks her body in a trunk, thinking she is dead. She wakes up later locked in the trunk, eventually dying inside it.35-years-later, this story is told among three school girls during a sleep over. One of them, Samantha (Kate Mara), had written an article in the school paper critical of football player's academic achievements and subsequently she, her friends and her brother David (Robert Vito) are treated as outcasts by the rest of the school. Samantha and her two friends, Martha and Mandy, jokingly conjure up Bloody Mary and the next morning all three are gone. After having been missing for one day, they reappear, waking up in an old deserted mill, with no knowledge of how they got there. While most suspect a hoax on the girls' part, Samantha and David suspect that it is some prank on the football team's part.While Samantha is haunted by visions of a dead girl bleeding from her head, several pupils die under mysterious circumstances resembling urban legends; for example, football player Roger (Brandon Sacks) burns in a sunbed. The next day, Heather (Audra Lea Keener), girlfriend to football captain Buck (Michael Gregory Coe), has spiders erupting from a swelling on her cheek, driving her to cut her face with a mirror. The following evening, football player, Tom (Nate Herd), is electrocuted while urinating on an old electrical fence, his ring finger being bitten or cut off.Buck blames these deaths on the Owens siblings. Before her death, Heather made up with Samantha and tried to tell her that this happened before. In her homework, Samantha finds notes sent to Heather about the disappearance of Mary Banner and the homecoming kidnappings of 1969, as well as notes referencing the events of the previous films. Browsing the school paper's archives, they find out that Mary was never found, that another victim committed suicide years later and that the third, Grace Taylor (Tina Lifford), still lives in town.They visit Grace, who claims that Mary, or rather, her "life force", is exacting revenge on the children of the five people involved in the kidnappings but cannot (or will not) reveal the names of the perpetrators. While Samantha is prone to believe her, David remains sceptical and thinks that Grace is more likely the killer. While sneaking around in Grace's house, he also found out that Grace produced or collected artwork on Urban Legend and identifies Grace as the originator of the notes sent to Heather. The siblings go to warn Buck, who admits that he and his mates orchestrated Samantha's disappearance and blames her for the death of this friends. He also reveals that his father, the football coach, was one of the kidnappers in 1969 but didn't hurt Mary. Samantha however suspects that the coach was the one that killed Mary as she saw him put flowers on her headstone earlier. Her stepfather, who overheard her, tells her to reveal any solid evidence she has.Meanwhile, an upset Buck tries to relax by drinking and watching movie in a motel. Falling asleep, he wakes up from hearing a dripping sound and discovers the corpse of his dog. He is attacked by Mary, who crawls out from under his bed and kills him with his broken bottle. Different rumours about his death immediately spring up.Both siblings are trying to find clues about the fifth remaining perpetrator, Samantha by browsing through old photographs, David by visiting Grace again. Grace still refuses to reveal the names but directs him to the school archives. Going through the archives, he suddenly finds out the identity of the fifth person and rushes home, but finds Sam gone and is suffocated by a hooded man. Samantha meanwhile has visions of Mary again, revealing that the girl was not dead when being locked in the trunk and also her whereabouts. She also visits Grace, who tells her to find and bury Mary's corpse and reluctantly agrees to drive Samantha to the school. While Grace is waiting in the van, Samantha finds the storage room and the trunk with Mary's corpse in it. The hooded man also appears and enters the storage room but Samantha locks him inside while carrying Mary's remains outside to the van.Finding Grace asleep, Samantha drives the van to the cemetery, where she begins to dig a grave for Mary under her headstone. Her stepfather, whom Samantha had phoned, also appears and helps her digging but suddenly hits her with the shovel. Pursuing his stepdaughter through the graveyard, Mr. Owens (Ed Marinaro) reveals that he was the one that locked Mary in the trunk and that he also killed his stepson, David. He finally captured her and is about to decapitate her when Mary, in her living form, appears. Smiling towards Samantha, she kisses him, then reverts back to her ghastly form and drags him with her into the grave.When Samantha wakes up, the grave is surrounded by police and medical personnel retrieving her stepfather's corpse. Mr. Owens is announced to have died of a heart attack while trying to dispose of Mary Banner's remains.

Question: What does Mary use to kill Buck?
Answer: broken bottle