Mr. Monk and the Red-Headed Stranger - S1-E12
Revealing mistake: In the scene where a man is streaking, he is carefully made to look naked. But when he is running through the park, there is one shot where you can see some black underwear.
Mr. Monk and the Red-Headed Stranger - S1-E12
Continuity mistake: In the closing scene with Willie Nelson, there are a few times when the clarinet music changes notes, yet Monk's fingers do not move. There is also one point where Monk takes a breath mid-note.
Mr. Monk and the Red-Headed Stranger - S1-E12
Continuity mistake: In the scene where Willie Nelson is rehearsing, his pigtails change position depending on the shot.
Mr. Monk and the Red-Headed Stranger - S1-E12
Continuity mistake: Before meeting Willie Nelson on his tour bus, Monk is outside the radio station. When a car comes past the shot shows from inside the car and we see Monk putting his right hand up to his forehead and touching it. In the next shot his hand is now further down his face and is not touching it anymore.
Mr. Monk and the Red-Headed Stranger - S1-E12
Plot hole: When Monk explains to Miss. Mass how she had murdered Sonny, a flashback of the crime shows that she isn't wearing gloves when she leaves the note to get him to go to the alley. Had the cops checked the note for prints, they would have shown Miss. Mass' fingerprints on it and knew she was responsible for Sonny's death.
Suggested correction: Just because they lifted fingerprints off the note, there wouldn't be a way to identify them as belonging to Ms. Maas if her prints aren't in the system. As a witness (and ruled out as a suspect because they thought she was blind), they wouldn't have fingerprinted her just because the found unknown prints and wanted to rule her out.
What about gun residue on the hands?