Deliberate mistake: When Henry Fonda decides to recreate the old witness' ability to get to the door in 15 seconds, he asks another juror to time his walk. The scene never cuts away, but the juror who times it says it took 41 seconds when in reality it takes exactly 31 seconds, you can time it.
12 Angry Men (1957)
1 deliberate mistake - chronological order
Directed by: Sidney Lumet
Starring: Henry Fonda, Martin Balsam, Lee J. Cobb, John Fiedler, Jack Klugman, E.G. Marshall
Deliberate mistake: When Henry Fonda decides to recreate the old witness' ability to get to the door in 15 seconds, he asks another juror to time his walk. The scene never cuts away, but the juror who times it says it took 41 seconds when in reality it takes exactly 31 seconds, you can time it.
Juror #6: You think he's not guilty, huh?
Juror #8: I don't know. It's possible.
More trivia for 12 Angry Men
Question: Did they ever look at the hole in his pocket that the knife supposedly slipped out of?
Answer: We have to assume that there was a hole in his pocket; we don't see it, but if the jurors are talking about it as a given fact, then it is likely that they checked it during the trial. However, it does not prove anything. It is easy to rip a hole in a pocket to produce an alibi. Also, it does not lower the extreme unlikeliness that someone else with another but similar looking knife stepped into the boy's apartment at around the same time he lost it. "One in a million," one juror said, and it was not really disputed. No. 8 gave his typical but meaningless "it is possible." Still, they went for an acquittal with these high odds against the boy.
Answer: If you're referring to the jurors, no. We see the entirety of their deliberations. If you're referring to the prosecution or defense, that is unknown. Given, however, that none of the jurors brought up the question, it's likely there was at least a check of his clothes to verify he had a hole in his pocket.
Given how easy it would be to simply tear a hole as an excuse, even if it was there, it wouldn't be much in the way of corroboration.
LorgSkyegon