Continuity mistake: When Josh throws the piece of fruit (or whatever it was) to break the lamp, Audrey checks out the lamp stand. In the shot where Walter first arrives and she's checking it out, it's all in one piece. But in another shot, it's suddenly all broken and a big piece is missing.
Other mistake: In the Peruvian Puff Pepper episode, Drake and Josh find the monitor in Megan's room. After they reveal the normal wall and the family leaves, Megan hits the button behind the picture to show the monitors. However, when Drake and Josh find out that Megan entered the salsa competition, they storm into her room, but the button is still revealed in the background.
Revealing mistake: When Josh says "I do not look good in pink panties" in the intro, he looks down below the camera at what we can assume is a script. He also cracks the tiniest smile near the cut, which is breaking character, as he was angry in that moment.