In the opening sequence, when Maggie is being scanned at the supermarket, instead of $486.52, the scanner reads "Read again".
At first, Marge needed a phone to hear Homer through the bulletproof window in the Prison's visiting room, but later, Homer is able to talk to her without the phone.
When Marge fires the prison guard's gun, the guard has long sleeves on his uniform. However, the sleeves become short when Marge is handcuffed. When Marge is escorted out of the visiting room, the guard's sleeves are long again.