The 1934 film:
- Playing Against Type: Leslie Banks, who often played bad guys (like Zaroff in The Most Dangerous Game and the leader of the gang of thugs in Hitchcock's later Jamaica Inn), is the hero here.
- What Could Have Been: One idea tossed around in the scripting stage was to have Abbott's gang hypnotize Jill and force her into being the assassin, a concept famously used decades later in The Manchurian Candidate.
The 1956 film:
- The Cast Showoff: Doris Day's agents demanded that she sing at least one new song, hence the inclusion of "Qué Será, Será" and "We'll Love Again."
- Contractual Obligation Project: Hitchcock owed Paramount one more film, and he resurrected the idea of an Americanized remake of the 1934 film, which he first hatched shortly after he moved to Hollywood.
- Playing Against Type: Ben McKenna is much closer to the usual all-American Jimmy Stewart character than Rupert Cadell, Jeff Jeffries or Scottie Ferguson, but his sometimes-tense exchanges with Jo show that he's not perfect. The scene where he insists on giving Jo some tranquilizers so he can tell her about Hank's kidnapping especially hints at a darker side of the character.
- Self-Adaptation: Alfred Hitchcock remade his 1934 film in 1956. He told François Truffaut that the first film was "the work of a talented amateur and the second was made by a professional". Nevertheless, Hitchcock preferred the earlier version, largely because it wasn't so polished.
- What Could Have Been:
- Ava Gardner, Grace Kelly, Kim Novak, Gene Tierney and Lana Turner were all considered for the role of Jo McKenna.
- Bernard Herrmann was originally going to compose an entirely new piece for the Royal Albert Hall scene, but he decided that the 1934 film's Storm Clouds Cantata worked fine for a climax, so he just wrote a new arrangement for it.
- Writing by the Seat of Your Pants: One of the difficulties Alfred Hitchcock faced with this film was that he had to start shooting before the script was finished.
- Working Title: Into Thin Air.