When Monk is following Rob Sherman at the Bay City Pier amusement park, there is a section where Rob passes two men in line, one with a light-colored jacket and the other with a purple shirt. He passes the same men twice, once with a ground-level camera and then again from a higher perspective.
When Natalie catches Clay kissing another girl, each shot focusing on Natalie (and eventually Monk) has passing cars getting into the intersection. However, each shot showing Clay, the cars are delayed and just heading toward the intersection.
In the opening scene where the murderer shoots the burglar, the murderer's slippers appear and disappear when he pushes the burglar over with his foot.
The murderer fires the gun twice. In both cases, the audio of the gunshot can be heard just before the muzzle flash instead of in sync with it.
When Monk and Randy Disher examine the bedroom, neither notices that there is another thermostat controller right next to the door, which would have completely nullified the killer's explanation of why his wife went downstairs in the first place.
Lt. Disher called the weapon the husband used a Glock 9mm. When the gun in question appears, it is not a Glock.
Around the 20:50 mark, when Julie is tutoring Clay in Spanish, they both pronounce the "h" in hermano and hermana, when in reality, the "h" is silent in Spanish. Julie should know this, as it is noted she is in Honors Spanish.
Despite Monk's fear of ladders and heights, when he's at the victim's apartment, he has no qualms about climbing onto a chair to get into the vent.