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.
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.
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.
According to the book "It's Only a Movie", Sir Alfred Hitchcock said, "There was an ending written which wasn't used, but I rather liked it. No one agreed with me except my colleague at home (his wife, Alma Reville). Everyone told me that you couldn't have a letdown ending after all that. Paul Newman would have thrown the formula away. After what he has gone through, after everything we have endured with him, he just tosses it. It speaks to the futility of all, and it's in keeping with the kind of naiveté of the character, who is no professional spy, and who will certainly retire from that nefarious business."
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.