The Hand

Jon Lansdale is finishing up a famous work of his called "Mandro", a Prince Valiant/Conan The Barbarian type of character. (In the film the actual "Mandro" artwork was drawn by real life Marvel Comics Conan artist Barry Windsor-Smith.) Lansdale is married to a beautiful woman named Anne (Andrea Marcovicci) and they have a child named Lizzie (played by Mara Hobel). While they are driving, Anne and Lansdale end up behind a slow-moving truck and an impatient driver behind them. In the heat of argument, Anne, who is driving, gets distracted and pulls out from behind the truck. Another truck comes up in the other lane. Anne attempts to get back behind the other truck but the impatient driver has pulled up too far. Lansdale waves his hand to the impatient driver to move back, and when she does not and Anne has to slam on the brakes, his hand is caught behind the truck, which also stops. The hand is severed completely in a bloody, violent scene. Anne attempts to find the severed hand but it is too late.
Lansdale then starts a painful adjustment to not having his right hand, which so happened to be his drawing hand. Anne also adjusts to her guilt of being responsible for the accident and tries to get closer with Lansdale. In a separate instance, he attempts to find the hand himself but does find his signet ring that Anne gave him. They move to New York and Lansdale is approached by his friend and agent Karen Wagner (Rosemary Murphy) to co-produce his comic strip with another cartoonist. But when the test boards are discovered marked up, the deal is off and Karen fires Lansdale. Lansdale, however, is certain HE did not mark them up and questions his daughter about the incident. He also loses the signet ring once again. During his recovery, Lansdale discovers that Anne has started moving away from him like before the accident. He becomes jealous of Anne's yoga instructor and also seems to begin a slow descent into darkness when an encounter with a homeless man (played by writer/director Oliver Stone) leaves the man dead at the "hand" of his former appendage. It's not entirely clear whether or not this was a real event or something in his mind. Lansdale also starts having hallucinations about different objects coming to life as a hand, like a shower faucet.
After his final meeting with Wagner, Lansdale comes forth with his intention to take an offer to teach at a small community college in California. The hand apparently cleans up the mess by the time Lansdale, along with Anne and Lizzie, who have arrived to celebrate Christmas, show up at the house. Not long after, Lansdale once again ends up at the bar with Brian. Confused that Brian should be off on his two-week vacation with Stella, Lansdale discovers that Brian has not seen Stella since the night she came to Lansdale's house. Lansdale awakens with his own hand (the one attached) around his throat while the police are skulking around. The sheriff, with Lizzie in tow, and his deputies attempt to ask Lansdale what happened. While he attempts to explain and he discovers that Anne is not dead, the officers notice a pungent smell permeating the area in the carport around the car, specifically from the trunk. Lansdale tries to prove that nothing is wrong by opening the trunk, only to find Stella and Brian's dead bodies inside. Lansdale looks and screams in horror.
In the final scene at a local insane asylum, a psychologist (Viveca Lindfors) is trying to communicate with Lansdale. She wants him to remember and admit that it was him, not his severed hand, who killed all the victims. He says that the hand wants to kill her because it hates her. Suddenly, the hand (which apparently existed all along) appears from behind the psychiatrist and strangles her. Lansdale, completely taken over by the essence of the hand, looks at her dead body and starts to laugh. He loosens the restraint on his other hand and gets up, presumably to escape from the asylum.

Question: What appears from behind the psychiatrist and strangles her?
Answer: The hand