Continuity mistake: In the scene in the basement, Chunk is about to drink from the water cooler bottle that is mostly empty. When he stands up and tries to catch it, it's more than half full. (00:40:25)
Continuity mistake: When everyone is searching upstairs and Miss Scarlet and Colonel Mustard start screaming, they all come running down. Yvette and Miss Scarlet have on flat black shoes, but right after the running shot is over, both are back in heels.
Continuity mistake: As Jason approaches the smashed barn door, some of the wooden planks in the left side of the door disappear between shots. (01:12:50)
Continuity mistake: During the scene where Fletch is at the hospital trying to locate Stanwyk's medical records, he drops lots of files on the floor and asks a nurse to sort them out. When he is talking to her he has a stethoscope in his ears, but when the camera moves behind him they are suddenly round his neck. Moments later they are back in his ears. (00:18:10)