Deliberate mistake: Why wouldn't Hank just use a credit card to cover the outstanding payment he owes on his insurace? It was established in the episode Rich Hank, Poor Hank that Hank has an emergency credit card and could easily use that and would be covered immediately. His panic over not having insurance would outweigh any problems he might have with using his credit card and the fact that he is dealing with an insurance company there is no conceivable way they wouldn't accept a credit card or ask if he has a credit card to cover the payment. The mistake seems to be deliberate as it sets the story up for Hank going somewhat over the edge with protecting the house.
King of the Hill (1997)
1 mistake in Mutual of Omabwah - chronological order
Starring: Brittany Murphy, Pamela Adlon, Mike Judge, Kathy Najimy, Johnny Hardwick
Dale Gribble: Boil up some Mountain Dew. It's gonna be a long night.
More trivia for King of the Hill
The Man Who Shot Kane Skretteberg - S2-E7
Question: When we first meet Kane Skretteberg, what is the song he and his band are playing in the garage? It is right before they start singing Funcenter over and over.
Answer: If you are talking about the "Thou shalt not do this, thou shalt not do that" song, I'm not sure if a song like that actually exists. Green Day, the guest voices on the episode, might have just been improvising to keep their appearance from being too obvious.