Sensory deprivation means removing stimulation from one or more senses, and the methods range from simple blindfolds, hoods, and earmuffs that cut off sight and hearing to elaborate rigs that also block smell, taste, touch, heat-sense, and even the pull of gravity. This film surveys where the technique turns up: alternative medicine clinics using flotation tanks, laboratory psychology experiments tracking what an understimulated brain does to itself, and interrogation rooms, including practices used by some NATO armed forces. It also covers the ganzfeld effect, where subjects face a constant, unvarying field of light or sound instead of an absence of stimulus, producing hallucinations and altered perception similar to true deprivation. The film weighs short-term effects like disorientation and hallucination against longer-term psychological damage, and sits with the ethical problem directly: a tool that can calm a patient in a flotation tank can also be weaponized against a prisoner. The throughline is the brain's dependence on a steady stream of sensory input, and what happens once that input stops.