Two Strangers on a Train: Will They Cross?
Dramatic Irony: Hitchcock spends the first 3 minutes of the film introducing audiences to both Guy and Bruno. Audiences know that the two will meet because of how Hitchcock introduces the two, but the characters don't know that they'll meet.
Myriam's Pregnancy
Dramatic Irony: The two men who accompany Myriam to an amusement park talk in wonderment about her consumption of ice cream, hot dogs and popcorn. Of course, the audience knows Myriam is pregnant, which explains her consumption of those foods.
Myriam's Rendezvous in the Fairground
Dramatic Irony: Myriam thinks that she is starting the process of dating a tall, normal man. However, audiences know that Bruno is aiming to kill Myriam.
"Bill Grogan's Goat"
Irony: The drunk man who sings "Bill Grogan's Goat" ironically leaves out two important parts of the song: 1) the part involving a train and 2) a very dark and violent (which would foreshadow things to come in the film).
Myriam's Murder
Dramatic Irony: Bruno's grandmother (who doesn't know that Myriam had been murdered the night before in an amusement park) asks to be taken to “maybe a good movie – with a murder in it – or maybe the amusement park”
A Trusting Psychopath?
Irony: Bruno, a cunning psychopath who would typically not easily trust someone, quickly trusts that Guy will commit murder (which he ultimately does not commit)