SnorriCam

The camera is strapped to the actor and points back at them, so the person is nailed dead centre and the entire world lurches behind them. It is the clearest way a film has of saying somebody has lost their footing.

The audience gets the feeling without the point of view. You are not seeing through the character's eyes. You are stuck to them, which is worse.

A harness holds a rig on the performer's chest or shoulders with the camera on an arm facing back at the face. The camera and the body are one object, so the body cannot move in frame.

Wide lenses are standard, because the camera is close and the frame still has to hold the face and some of the background. That width is also what makes the background swing so hard.

Walking is the engine. Every step, sway and stumble transfers straight into the picture, and the wilder the movement the stronger the effect.

Use it on collapse: panic, withdrawal, obsession, a character walking somewhere they should not be going.

Do not use it quietly. The shot is extreme and it tells the audience the film has changed gear, so it needs a reason.

A point of view shot looks out through the character's eyes, so the character is not in the frame at all.

A SnorriCam looks back at the character, so their face is the fixed centre of the picture. If you can see the person's face, it is a SnorriCam.

Darren Aronofsky uses the rig repeatedly in Pi (1998) and Requiem for a Dream (2000), strapping the camera to characters as they come apart. The face stays locked in the middle of frame and the city behind it will not hold still.

The background stays calm, which makes the shot an ordinary centred close-up. Say the world swings violently behind the subject as they walk.

The second failure is a subject who moves in frame. Say the subject is locked dead centre and motionless relative to the camera, because the rig makes that physically true.