Right at the beginning of this episode, Mr. Strickland makes Hank take 2 weeks off because he hasn't taken a day off since Bobby was born. That can't be true, since last season in Pretty Pretty Dresses, Mr. Strickland made Debbie clear out Hanks vacation days so Hank to take a bunch of days off to watch Bill and keep him from killing himself.
The poster on the wall by the door alternates between "Chamfer" and "Canfer".
In the episode where Hank becomes a shop teacher (S4, E4, Little Horrors Of Shop), Hank is alerted by Clark Peters that something has happened with Bobby. When Hank and Clark run down the hallway, Hank's pants are brown. Just before Hank stops, his pants magically turn to blue in front of your eyes.