Throughout the film, hospital staff frequently address Teddy by name or "Marshal" before he even introduces himself. Subtitles make these "slips" more prominent, suggesting a level of familiarity that supports the theory that Teddy has been a patient for years.
Two US marshals are sent to a mental institution on an inhospitable island in order to investigate the disappearance of a patient. "Shutter Island" Review - The Independent Critic shutter island with subtitle
Subtitles can help viewers track the repeated mentions of fire (representing Teddy's fantasy) and water (representing his repressed reality/trauma). Throughout the film, hospital staff frequently address Teddy