In a conversation with François Truffaut, Sir Alfred Hitchcock said that he included the fight scene deliberately to show the audience how difficult it can be to kill a man, because several spy thrillers at the time made killing look effortless.
Sir Alfred Hitchcock was so unhappy with this movie that he decided not to make a trailer with his appearance in it.
Steven Spielberg told James Lipton on Actors Studio (1994) that as a young man he snuck onto the soundstage to observe filming, and remained for forty-five minutes before an assistant producer asked him to leave.
The idea behind this movie came from the defections of British diplomats Guy Burgess and Donald Maclean to the Soviet Union in 1951. Sir Alfred Hitchcock was particularly intrigued about Maclean's life in the Soviet Union, and about Melinda Marling, Maclean's wife, who followed her husband behind the Iron Curtain a year later with the couple's three children.
Bernard Herrmann wrote the original score, but Universal Pictures executives convinced Sir Alfred Hitchcock that they needed a more upbeat score. Hitchcock and Herrmann had a major disagreement, the score was dropped, and they never worked together again.
Alfred Hitchcock: Early in the movie sitting in a hotel lobby with a baby on his knee. He transfers the baby to his other knee, and then rubs his knee, as if disdainfully looking at something the baby has done to it.