Continuity mistake: When Homer runs towards Moe's Tavern with his new head of hair, he looks into the window and you can see there is an empty beer bottle on the window sill next to him. When the camera changes to inside the Tavern in the next shot, the beer bottle has gone.
Continuity mistake: When Homer is watching TV at the beginning of the episode, Marge takes away his plate of leftovers and puts an ice-cream sundae in front of him on his tray. When we see him a few shots later, his plate is now back on the tray with the ice-cream sundae on top of it.
Continuity mistake: When the doctor brings the "Hair in a Drum" product from under his desk, you can see in front of Homer there is a bottle of Dimoxinil and two gravity boots. When we see a close of the product in the next shot, the bottle and gravity boots on the desk have disappeared.