Fair Fight - S6-E5
Continuity mistake: When Johnny and Roy are in the ER after the cave-in rescue, while they're talking to Dixie and Brackett, we can see how long Johnny's hair is. After they get back to the station, when the guys decide to name the dog Henry, there's a closeup of Johnny and now his hair is much shorter and even layered at the sides. Additionally, the dirty areas on his shirt change.