Continuity mistake: When Natalie props the get-well card up on Monk's bureau, it's partially open. The moment the shot cuts to a different angle, it's completely closed. (00:10:15)
Other mistake: During the flashback of the perpetrator beating up the victim with a baseball bat, the shot is visibly spliced and there's a jump cut while he is between swings of the bat. (00:32:50)
Continuity mistake: After DeLancy loosens the tie Stottlemeyer gave him, the position of the knot changes without him touching it.
Plot hole: When Stottlemeyer and the other cops arrive at the recycling center, the patrol car's siren turns on and off. The killer had said to Monk that if he called the cops, he'd kill Natalie. Coming to a hostage situation with the siren going would be a really bad idea. (00:37:45)
Answer: The two men are trying to work out a secret deal between them without involving the union, which means the workers' interests aren't being represented and defeats the whole purpose of a union. The mayor would lose labor's support and Cusack's union troubles would just be starting.
Captain Defenestrator