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.
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.