When the students watch Britta and Shirley take on the last few storm troopers Abed and Annie are standing very far apart and then in the next instant they are standing side by side.
The amount of paint on characters changes from scene to scene. It also appears wet and then instantly dry. A prime example is Abed in the library, when only half of his face is covered in wet paint. Very soon after his whole face is painted and the paint appears very dry.
Pulling a fire alarm switch will not activate the sprinkler system, just the alarm bells/horns and strobe lights.
When the usurpers from City College topple the Luis Guzmán statue, it folds in half when it hits the ground. But this is Greendale -- it's no surprise that the statue would be made as cheaply and of the thinnest material possible.
When Magnitude throws himself upon the remote control grenade robot, pink stains from previous takes are visible along the sides of his clothes.