Mr. Monk and the Red Herring - S3-E10
Revealing mistake: When Julie's teacher is searching the name 'Larry Tilburn', he isn't typing into a search engine, virtual encyclopedia, or anything of the type, the computer just shows a blue screen with a popup message in the middle.
Mr. Monk and the Panic Room - S3-E2
Revealing mistake: Throughout the episode, the panic room door is made to look metal. But later when a hole is cut in the door, you can easily tell by looking through the hole that it is wood.
Mr. Monk and the Panic Room - S3-E2
Revealing mistake: In the scene where Darwin and Monk are in the kitchen and Monk calls Dr. Kroger. Darwin pulls the phone out of the wall, but there is no line from the phone to the jack in the wall.
Suggested correction: The phone is a wall type that connects directly at the back. The jack on the wall is wired, and the phone connects when it's mounted. This was a feature of many wall mounted phones as you didn't want exposed wires.
Mr. Monk Gets Stuck in Traffic - S3-E13
Revealing mistake: The VW Beetle that slides out of the dump truck and rolls over is noticeably not the same car the victim was driving earlier. It's a lighter color, and is already badly dented, even before it's wrecked.
Mr. Monk Gets Stuck in Traffic - S3-E13
Revealing mistake: When we see a shot of Steve in his car while in the dump truck, it's shot in a studio and the shot is reused each time we see Steve in the car. The shadow is completely different and at one point, when they show Steve in the car with the car and truck bouncing around, you can tell the image is just shaken, rather than the dump truck actually bouncing. There are loose chains hanging off the inside walls that don't move or sway at all.
Mr. Monk Takes Manhattan - S3-E1
Revealing mistake: Monk's reaction to the gunshots begins just before the gunshots go off. (00:03:55)