Rachel Solando's return (situational irony)
Scorsese initially frames the film's plot as one where a U.S. Marshal named Teddy Daniels is investigating the disappearance of a patient named Rachel Solando. Thus, in an example of situational irony, the audience is surprised to learn from Dr. Cawley that she has in fact been found so early in the story.
McPherson's disarmament (dramatic irony)
Practically all of Shutter Island can be considered one long feat of dramatic irony as soon as the audience understands that everyone is performing for Teddy's benefit, beginning with Deputy McPherson's welcoming of the men to the island. McPherson is, in fact, acting in order to help Teddy fulfill his fantasy as a visiting U.S. Marshal, even demanding to confiscate his plastic gun.
Group therapy (dramatic irony)
Teddy's interviews with Mr. Breene and Mrs. Kearns are tense and awkward, seemingly because Teddy is a U.S. Marshal visiting from the mainland. However, in an example of dramatic irony, a practiced viewer of the film realizes this is because Teddy is a fellow Ashecliffe patient who has been given an alarming amount of control over the facility under Cawley's direction.
George Noyce (dramatic irony)
Teddy's encounter with George Noyce in Ward C is the first time Teddy realizes that Chuck and the rest of the Ashecliffe employees are implicated in a plot against him, but he still thinks that they are covering up a Nazi-engineered conspiracy. However the clued-in viewer, in an example of dramatic irony, knows that Teddy is in fact an Ashecliffe patient given free rein so that he might be spared a lobotomy.
"Why are you all wet, baby?" (situational and dramatic irony)
Upon first viewing, this line spoken by Dr. Cawley exemplifies situational irony because it arrives at an unusually anti-climactic moment and sounds strangely intimate. Upon a second viewing however, this line becomes an example of dramatic irony, because the viewer knows Cawley is in fact quoting Teddy himself, from the day his children died.
