Trilogy of Terror

"Julie"[edit]
Chad (Robert Burton) is a college student with a crush on his English teacher, Julie Eldrich (Karen Black). During one class, Chad is distracted by Julie's thigh as she sits on her desk and daydreams about her. After Chad reveals his fantasies to his friend Eddie (James Storm), Eddie describes Julie as "ugly" and discourages him from becoming romantically involved with teachers. Later that evening, when Julie is undressing in her room, Chad watches her through a window. The next day, he asks Julie out on a date. She initially refuses, but later accepts the offer.
During the date at a drive-in theater, Chad spikes Julie's drink, rendering her unconscious and drives her to a motel. After checking them in as husband and wife, he photographs her in a variety of sexually provocative positions. She begins to regain consciousness, and Chad takes her home, explaining that she had just fallen asleep.
After developing the photographs in his darkroom, Chad shows the pictures to Julie. She is furious and threatens to call the police. Chad blackmails Julie into submitting to his romantic attentions, and she reluctantly agrees.
After several weeks of this, Julie announces, "The game is over." She reveals that it was actually she who had manipulated Chad in an elaborate role play of her own design. "Did you really think that dull, little mind of yours could possibly have conceived any of the rather dramatic experiences we've shared? Why do you think you suddenly had the overwhelming desire to see what I looked like under 'all those clothes?' Don't feel bad... I always get bored after a while."[1] Chad realizes that Julie has poisoned his drink, and then he dies. Julie drags his body into the darkroom where she sets fire to the offending photographs. Chad's death is later reported in local media as a house fire. Julie adds the newspaper story to a scrapbook of articles depicting students who met similar fates. There is a knock at the door, and another student (played in a bit role by Gregory Harrison) in need of a tutor enters.
"Millicent and Therese"[edit]
This tale of sibling rivalry focuses on sisters Millicent, a repressed and prudish brunette; and Therese, a worldly, seductive, and free-spirited blonde. Both roles are played by Karen Black.
Millicent is determined that Therese is evil, and plants a voodoo talisman to kill her. When Millicent's friend Dr. Ramsey enters the house, he finds Therese dead on her bedroom floor with the doll next to her; Millicent is nowhere to be found. Dr. Ramsey reveals, as the family doctor, that "Therese" and "Millicent" are the same person; Therese suffered from multiple personality disorder brought on by the fact that "Therese" slept with her father and subsequently killed her mother - and "Millicent" was an alternate personality with a repressed sexuality to cope with the horror of her actions. The recent death of the father unhinged her further and the "murder" was actually a form of suicide.
"Amelia"[edit]
"Amelia" was filmed as a one woman play, with Karen Black as the only actor. It was also the only film of three to be adapted by its author, Richard Matheson, who based "Amelia" on his short story, "Prey".
Amelia lives alone in a high-rise apartment building. She returns home after shopping with a package. Inside is a Zuni fetish doll, crafted in the form of a misshapen aboriginal warrior equipped with razor sharp teeth and a spear. A scroll comes with the doll, claiming that the doll contains the actual spirit of a Zuni hunter named "He Who Kills", and that the gold chain adorning the doll keeps the spirit trapped within. As Amelia makes a call to her mother we learn that she suffers from her mother's overbearing behavior. Amelia struggles to justify her independence and attempts to cancel their plans for the evening because she has a date. The moment Amelia leaves the room, the Zuni doll's golden chain falls off without her knowing.
Later, Amelia is preparing dinner, using a carving knife. She enters the darkened living room, and realizes the doll is not on the coffee table. Amelia hears a noise in the kitchen and when she investigates, the knife is missing. Returning to the living room, she is suddenly attacked by the doll, which stabs at her ankles viciously. She attempts to flee, but the doll chases her around the apartment. In the bathroom, Amelia envelops the doll in a towel and attempts futilely to drown it in the bathtub. She later traps it in a suitcase, but the doll begins cutting a circular hole through the top of suitcase with the butcher knife. After several more vicious attacks, Amelia manages to hurl it into the oven and listens to it howling and screaming as it catches fire. Soon the screams die down and eventually stop. She opens the oven to ensure that the doll is "dead', and a cloud of black smoke billows out. Inhaling the smoke, she is suddenly overcome.
We see Amelia place another call to her mother. In a calm, controlled voice, she apologizes for her behavior during the previous call, and invites her mother to visit her home for dinner. She then rips the bolt from her front door and crouches down low in an animalistic manner, hiding in the corner with a carving knife. She stabs at the floor with the weapon, grinning ferally and revealing the horrific teeth of the Zuni doll whose spirit now inhabits her body.

Question: Who played both roles of the sisters?
Answer: Karen Black