Hypnosis is an altered state of consciousness that makes the subject highly susceptible to suggestion. This entry contains ideas for what this could look in the various scenarios (hypnosis in a therapy session, onstage as part of a performance, etc.), as well as behaviors that might result. In fiction, there's leeway as to how a hypnotic state can be used, but we recommend researching what is and isn't possible so you don't wander too far afield.

Eyebrows pulling together
Slackness in the face
Becoming expressionless as the trance takes hold
Blinking less frequently
Eyes moving beneath closed eyelids
Swallowing less frequently
An overall stillness
The skin becoming paler or flushed (due to blood flow changes throughout the body)
Tension disappearing from the shoulders
The body going limp
The character slumping over while seated
The arms hanging at the character's sides
The head rolling to the side or nodding forward
Being unresponsive to loud noises
A cessation of common tics and twitches that usually assail the character
When the eyes are open, having a vacant or inward look (waiting for instruction)
Reddened eyes
The character responding to the hypnotist's prompt after a slight lag
Responding to questions automatically
Changing behavior based on an instruction or pre-determined cue (a sound, word, sentence, or action)
Reacting to hallucinatory sensory stimulation (behavior matching the emotional trigger)