Excision (2012)

Pauline is a disturbed, delusional high school student who aspires to become a surgeon despite her dysfunctional family life. Her younger sister, Grace, has cystic fibrosis, and the girls' controlling, strongly Christian mother Phyllis shares a strained marriage with their father, Bob. Pauline often has vivid dreams about herself and others being mutilated with excessive amounts of blood, after which she wakes panting in an orgasmic state.

Pauline decides to lose her virginity to a classmate named Adam, choosing to do so while on her period because of her fascination with blood. She and Adam have sex, and as she has an orgasm, she imagines herself choking Adam and the bed filling with blood. She then asks Adam to perform oral sex on her. Unaware that she is menstruating, he obliges, only to run to the bathroom in disgust when he tastes the blood.

During a sex education class, Pauline examines a sample of her own blood under a microscope, mistakenly believing she can detect sexually transmitted diseases that way. She later approaches Adam while he is with his girlfriend Natalie and alludes to their encounter, causing Natalie to break up with him. Natalie and her friend later throw toilet paper and spray paint profanities on Pauline's house. At school the next day, Pauline assaults both Adam and Natalie, and is consequently expelled.

Pauline overhears her parents discussing Grace's doctor's plans to put her on a waiting list to receive a lung transplant. That night, Grace suffers a severe coughing fit. In the morning, Pauline drugs Bob's tea and ties him up before confronting a neighbor who had rebuffed Pauline's earlier attempts at friendship. She lures the girl to her backyard and uses chemicals to knock her out, subsequently drugging Grace.

Pauline shaves her head before attempting to transplant the healthy girl's lungs into Grace's body, placing Grace's diseased lungs on ice, and stitching both girls up. Phyllis arrives home, panics at the sight of Bob bound and gagged, and begins frantically searching the house for her daughters. She finds Pauline in the garage with the bodies. Pauline explains that it is her first surgery and urges Phyllis to take a closer look. Phyllis screams hysterically before embracing her. Pauline at first smiles proudly, but then begins to wail as she seemingly realizes what she has done.