Revealing mistake: Whenever Dr. Nemur is smoking, you can tell the cigarette's not lit, because you can't see any smoke. When Mrs. Kinnian smokes in the movie, plenty of smoke is visible.
Charly (1968)
1 revealing mistake
Directed by: Ralph Nelson
Starring: Cliff Robertson, Claire Bloom, Lilia Skala, Leon Janney
Factual error: There's one scene where Charly's just woken up from his surgery. The next scene shows him working on a puzzle, and he has a full head of hair and no bandages. If he'd just got brain surgery, don't you think he'd still be wearing bandages or at least have his head shaved?
Charly Gordon: That, that is, is. That, that is not, is not. Is that it? It is.
Trivia: This movie is based on the book "Flowers for Algernon." The Simpsons also spoofed this in an episode called "HOMR." (The one where they find that Homer has a crayon up his nose.).