When Monk and his crew enter Donovan's office at the end of the show, there are sockets in the top of Donovan's chair for a headrest, but no headrest. In the next shot, the headrest is there.
When Monk and Natalie first look at the blood-stained seat in the company car, the seat belt buckle is resting on the edge of the seat. Seconds later, when Monk reaches in to pull the seat belt out to show it to everyone else, the seat belt is fully retracted and he has to reach behind the seat to retrieve the buckle end.
The amount of charcoal dust in the palm of Monk's hand decreases, though he never wiped it off.
During the conversation Monk and Natalie are having with the cult members at the recruiting station, before he gets on the van with them, a green bus with Culver written on it, and a red Metro Rapid bus drive by. These buses are Los Angeles area buses, but the show takes place in San Francisco.
Captain Stottlemeyer says Father gets a cortisone shot every week for his bad back. Epidural steroid shots are limited to three per year.
When Monk is explaining about the red-light photo, he says "A picture of you," and points to the photo. Then he moves his finger to the right and says "And her." That is the reverse of the real photo. Monk would never get a detail like that wrong.