The hamster Lisa gets for her experiment is light gray but when Bart uses it for his project it's brown.
The two men sitting behind Homer and Barney at the baseball game are wearing purple and blue shirts during the commentating but in the next shot when Homer says "I never realized how boring this game is" their shirt color's change to red and white.
When the barflies groan after Moe announces that Homer's back, Larry appears at the bar twice.
Homer reminisces about buying his first beer with a very obvious fake ID but it's also clear in the same scene the liquor store clerk is already suspicious of Homer.