Continuity mistake: When Cho finds Archie's notebook under the bed, he turns to near the end and starts reading Archie's entry. But the position of where Cho has the notebook open changes, depending on the camera angle.
So Long, and Thanks for All the Red Snapper - S4-E22
Continuity mistake: Cho opens the vent with a screwdriver and hands it back to the landlord (who pockets it). In the next shot Cho has it in his hand again finding the hidden drugs. (00:10:00)