Final answer:
The device used in Requiem for a Dream to achieve subjective shots is called a SnorriCam, which keeps the actor's face stationary while the background moves.
Step-by-step explanation:
The apparatus used to strap a camera to an actor's chest to achieve a subjective shot is known as a SnorriCam. This device allows the camera to remain fixed on the actor's body while they move, creating a dynamic and often disorienting perspective that keeps the actor's face stationary in the frame while the background moves around them. The effect is used in Requiem for a Dream to convey the inner experiences and psychological state of the characters.