Continuity mistake: When Natalie puts out the fire with the extinguisher, the nozzle is still pushed down when she uses it, but when she puts it on the table, in the next shot the nozzle is fully extended. There are a number of times during the scene, when Monk is trying to figure out how to use it, where the nozzle's position keeps changing between shots.
Continuity mistake: At the science fair, after Lyle Peck lights the poster on fire he puts the Bunsen burner onto the table a little away from its original position but when the camera angle changes it is back where it originally was, under the beaker and stand.
Continuity mistake: Monk empties a pocketful of pushpins onto the science teacher's counter top. One rolls to the very edge, separate from the others. A few minutes later, the stray pin is missing. Just before Monk and Natalie leave, however, it reappears on the counter edge.