Mr. Monk Goes to the Asylum - S1-E6
Factual error: The woman who accuses Monk of stealing her necklace shouldn't have the necklace inside the asylum in the first place. For both safety and insurance reasons, patients in mental facilities aren't permitted to keep any potentially harmful jewelry, including pins, broaches, earrings, belts, beads and necklaces.
Mr. Monk and the Candidate (1) - S1-E1
Factual error: When the rifle is identified as a "Weatherby Fibermark", Monk and Randy say it's a British rifle. But Weatherby is an American company.
Mr. Monk and the Airplane - S1-E13
Factual error: When the flight attendant announces that "they have been asked to return to the gate" the French pilot and his mistress are already celebrating with a glass of wine, but that is impossible since drinks are only served after the take off phase when the plane has reached its traveling altitude. (00:41:15)
Mr. Monk and the Airplane - S1-E13
Factual error: Though anti-freeze is lethal it does not kill quietly and fast but rather agonizingly, painfully and slowly, inducing vomiting and fever. (00:30:30)
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