Continuity mistake: In the episode where Lois takes revenge on the four girls who pranked Reese, Lois and Reese use a makeshift catapult to launch paint balloons at one of the girls and her date. The first balloon hits the girl, covering her left shoulder with pink paint. In the shot where her date gets hit with a balloon, her shoulder is no longer covered in paint. Some of the paint blotches change size and shape on both her and her date throughout this scene as well.
Continuity mistake: In the scene where Lois finds out about Francis escaping, there are three orange mugs hanging from a rack by the phone. When Lois reaches for the phone to call the police, she makes the middle one start swinging. She and Hal sit down, and the end mug has moved from the rack into a box on the kitchen counter. Also, the mugs are hanging still. Towards the end of the scene, the "fallen" mug is back on the rack, and the middle mug is swinging again.
Continuity mistake: Malcolm's seat belt changes from on to off the first scene with him and his mom in the car. When it's a shot from the front it's on, but when it's a shot from the side (from the driver's/mom side) you can see that the part of the seat belt that's going across is now behind Malcolm, instead of on him like it was a second ago. This changes back and forth.
Continuity mistake: When Lois and Kitty Kenarban (Stevie's mom) are at the table in the restaurant, while Hal and Abe sit at the bar, things on the table change position or disappear and reappear between shots. Same thing happens at Malcolm's table with Reese and Stevie.
Continuity mistake: When the "Krelborne" teacher comes to the house to tell Lois that Malcolm is gifted, Lois comes to the door naked and puts her arm up on the doorway. On the shot from behind she has her hand low (about where her waist is) from the shot from the front she has her hand up high (above her head).