Revealing mistake: Towards the beginning of the film, when Hannay has been arrested for the murder of Scudder he is being interviewed by Chief Superintendent Lomas. Hannay removed the bullets from Scudder's pistol whilst he was staying in his apartment, and Lomas is shown putting them on the table. One of the bullet casings has a hole drilled through the center of it, a typical method used to identify inert rounds as being safe to handle.
The Thirty Nine Steps (1978)
1 revealing mistake - chronological order
Directed by: Don Sharp
Starring: David Warner, Robert Powell, Eric Porter, Karen Dotrice
Other mistake: After David Warner kills a man with his long thin sword, he pulls the sword out and puts it back in its scabbard, but there's no blood on the sword or anywhere.
More trivia for The Thirty Nine Steps