Continuity mistake: When Audrey eats her gelato on the steps of the Spanish Plaza, if you look closely, the time is about 12:00 when she buys the cone. However, when she starts eating it, you can see that it's past 3:00.
Continuity mistake: When Audrey and Gregory are saying goodbye in the car, there are two shots where rain is visible outside the car window behind them. When Audrey gets out and walks away, however, it's dry outside.
Trivia: When Gregory Peck puts his hand into the Mouth of Truth and withdraws it (hand tucked into sleeve) the scream that Audrey gives is real. The prank was unscripted, but the reaction so perfect that it was left in.
Trivia: Because he'd been blacklisted by the HUAC (House Un-American Activities Committee) in 1953, co-writer Dalton Trumbo's name didn't appear in the credits for this film until its DVD release in 2003.