Mickey and Eddie Are Brothers (Dramatic Irony)
This is the central irony of the musical. Unbeknownst to them, Mickey and Eddie are actually twin brothers separated at birth. They become "blood brothers" after discovering they share a birthday and develop a long-lasting friendship, all the while not knowing that they are actual brothers. In this instance of dramatic irony, the audience understands the nature of their real relationship while they remain unaware.
Mrs. Lyons Says Superstition Will Kill the Boys (Situational Irony)
Early in the musical, Mrs. Lyons says the boys have to be kept apart, because otherwise they will cause each others' deaths. However, she actually instigates the murder by telling Mickey that Eddie is having an affair with Linda. In this moment of situational irony, the audience expects that Mickey and Eddie will be killed in some kind of twist of fate, but it is actually a scene set in motion by the person who claimed to be protecting them from harm.
The Policeman Doesn't Scold Eddie (Situational Irony)
After getting angry with Mrs. Johnstone about Mickey's behavior, the policeman adopts a very warm and friendly tone with the Lyons family. He says that he thinks that he just had a misunderstanding with Eddie and that it surely won't happen again. Despite behaving in the same manner as Mickey, Eddie is left off with little more than a polite warning as a result of his social status. In this instance of situational irony, the audience expects the police to speak to Mrs. Lyons with a similar degree of harshness, but he instead is exceedingly friendly.
Eddie Thinks the Locket is Just a Picture of His Friend (Dramatic irony)
Mrs. Johnstone gives Eddie a locket that she says is a picture of her with Mickey. She says she hopes it will serve as a memento of their friendship. However, as suggested by Mrs. Lyons' shock when she sees it, the locket is likely a picture of Mrs. Johnstone and Eddie as a baby. Eddie thinks the locket is a picture of his friend and his mother while the audience is aware that it is probably of him and his biological mother.
