Character mistake: Season 3, episode 12, "Mr. Monk Gets Cabin Fever": When Randy Disher is having Chinese food in his apartment with his new girlfriend, he gets a fortune stating that he is going to get money from his uncle. Randy says that he doesn't have an uncle. In Season 5, episode 14, "Mr. Monk Visits a Farm", Randy inherits a farm from his uncle who appears to have committed suicide, but was actually murdered.
Continuity mistake: After Stottlemeyer says "Well I'm gonna make the most of it" (when he is talking to Monk in the backyard of the cabin and Monk is cleaning) he looks a little to his left and opens a beer can while his mouth is shut. In the next shot he is looking in a different direction and is smiling a toothy grin.
Other mistake: When Stottlemeyer is about to eat his cake he is looking at Monk. Shortly before he starts to pick up a piece of cake you can see he is pretending to chew a piece in his mouth. Throughout the scene you can see Stottlemeyer's face and the cake. At no point before he pretends to chew does he put a piece in his mouth.
Factual error: Randy calls the cabin and gets a "not in service" message. But he should have heard an unanswered ring instead. The FBI agent tore the cord from the wall, which in the US does not generate a "not in service" recording. That only occurs when the phone company cuts off your service due to non-payment or cancellation.
Continuity mistake: When Randy and his 'girlfriend' are having take-away (take-out) food, the girlfriend says, "Before he died, he said he's always look out for me". As she says this, her arms are resting on the table, but in the next shot her elbows are on the table and her hands are together just under her chin.