Continuity mistake: When Natalie and Al are struggling, the gun lands on the table and there's a basket of corks. Somehow when Al gets the gun, the basket is tipped over and the corks are on the table. But after Monk hits Al, the corks are all back in the basket, which is upright.
Continuity mistake: After Sharona's class, she's holding her book upside down when talking to the teacher (so the binding can be seen). In the next shot, the book is held right side up. Afterwards, when she's walking away, the book is upside down again.
Continuity mistake: When Monk and Sharona talk to Sylvia in the prison library the second time, the books on her desk change in various shots. At first, you see 3 piles of books, all with blue books on top. In the next shot the blue book closest to her is gone. In the next shot, she's straightening a red book next to her, but it goes back to being crooked.
Continuity mistake: When the Captain is eating his sandwich while talking to Monk, the position of the sandwich and amount eaten keeps changing. He'll have it in his hand, but in the next shot it's on the plate. And you see him take a 2nd bite, but later only 1 bite has been taken.