In every scene that Cleveland is in after he loses his moustache, his belly button is missing.
Cleveland Junior sits at a table with 6 empty beer bottles but when he clears the table there are only 5 bottles. And when he brings that tray to Gus, there are only 3 beer bottles on the tray.
When we see a close up shot of the box of crayons Gus puts on the bar, the one he grabs and the one he holds up are not the same color. Also, the peach crayon Cleveland Jr. is using changes color from a lighter color to a darker color.
The crayon piece that Cleveland slaps out of Junior's hand falls on the floor but vanishes when Gus suggests Junior work at the bar.
When the guys are at the Broken Stool after Cleveland gets his fake mustache, there are 16 bottles of beer in the scene, 12 bottles on the table. Gus brings 4 more, making 16 on the table. However when the guys start to fight there are 13 bottles on the table and when the shot widens, there are 10 on the table.