When Professor Duncan writes the word "something" on the blackboard, it is initially what appears to be a "p" instead of a "g", but in later shots it is changed to a "g".
In the scene where Professor Duncan circles and underlines the "Anthropology 101" written on the board (around 4-5 minutes in), there is one line under "Anthropology 101", then when Chang enters there are two lines. When the pictures cut to the Professor moments later, it goes back to being only line.
While driving to the morgue, the bubbles in the lava lamp change between shots.
Greendale is suppose to be around Denver, CO, but downtown LA is clearly seen in the background.