The House of the Devil

In the 1980s, after her landlady (Dee Wallace) gives her an extension on the deposit for her new apartment, college student Samantha Hughes (Jocelin Donahue) takes on a babysitting job for Mr. Ulman (Tom Noonan) and his wife (Mary Woronov). Ulman asks to meet her but stands her up, later apologizing and offering to pay double the original salary. Samantha accepts and gets a ride to the remote mansion from her best friend, Megan (Greta Gerwig), who expresses her distrust. At the house, Mr. Ulman pulls her aside and reveals that he does not have any children to be monitored; the babysitting job is to attend to his wife's ailing mother. Samantha balks but finally agrees, if he will pay her $400, a significant increase in her pay. Megan immediately leaves, citing Ulman's lies and peculiar behavior, but she reluctantly promises to pick up Samantha later. Samantha stays, after accepting the money. On the way home, Megan stops in her car to smoke a cigarette. When her car lighter will not work, a stranger (A.J. Bowen) suddenly appears out of nowhere, startling her, and lights her cigarette for her. When Megan reveals that she is not the babysitter hired by the Ulmans, she is abruptly shot and murdered by the stranger.
After ordering a pizza, Samantha dances around the house while listening to her Walkman, accidentally breaking a vase in the process. While cleaning up the mess, she discovers a cupboard filled with old family photographs. In one photograph a different family than the Ulmans' stands next to the Volvo she and Megan saw upon pulling up to the house. An additional peculiar detail is that the family in the photograph has a young son. This seems unlikely as the Volvo is a new car and Mr. Ulman stated that although they had a child he was now grown. Samantha draws a rash conclusion that Ulman has possibly murdered the original mansion owners and stolen their car. In a panic she dials 911 but eventually manages to calm herself down. The pizza is finally delivered by the stranger who had killed Megan. Drugs in the pizza cause Samantha to pass out, just as she discovers activity behind a door leading to the third floor. When she comes to, she finds that she has been bound and gagged in the center of a Pentagram. As a lunar eclipse darkens the night sky, Mr. and Mrs. Ulman, along with the stranger, who is actually their son Victor, begin a bizarre ritual. Mother (Danielle Noe) is revealed to be a grotesque, witch-like figure. As part of the ritual she slices her arm and pours the blood into a goat skull. She uses the blood to draw occult symbols on Samantha's stomach and forehead, and forces Samantha to drink her blood from the skull. Samantha manages to escape halfway through the ritual, killing Mrs. Ulman and Victor, but horrific images begin appearing in her mind. Mr. Ulman chases her out of the house and through a nearby cemetery. There, he tells her she was chosen. Samantha threatens him with the gun used to kill Megan, but Ulman passively accepts his fate, claiming to be a messenger and gloating that she's too late. Instead of shooting him, she shoots herself in the head, to Ulman's horror. The scene cuts to a broadcast about the strange lunar eclipse the night before, which has confounded scientists due to its abrupt ending, as Samantha is revealed to be in a hospital bed, in bandages. A nurse walks in and pats the unconscious Samantha on the stomach, reassuring her that "You will be just fine. Both of you."

Question: What does Samantha accidentally break while dancing?
Answer: A vase