Mr. Monk Meets Dale the Whale - S1-E4
Revealing mistake: When Monk is showing how Dale and his Doctor murdered the judge one can see that the knitting of the right chair is already cut to ensure that the policeman will fall through it when he later steps on it.
Revealing mistake: While Horatio and Alexx are examining the prostitute's body, you can see the corpse breath in a side view.
Revealing mistake: As Bunk is ordering ballistics to rush comparisons, the dead bodyguard is breathing during the scene. (00:01:55)
Revealing mistake: The left pinball in the arcade (which later disappears) has the body of a "Star Trek TNG" machine - but the backglass is purely fictional. (00:17:45)