Lane's Korean replacement asks for a Monte Cristo sandwich, but in a previous season, when Luke gets new menus, it's said that he took off that sandwich.
When Lane is talking to Zack, two sauce bottles (red and yellow) appear on the middle table.
When Lane and Kyon are talking at Luke's, you can see a semi-loose strand of hair on the left side of Lane's head. When she walks over to the boys, she doesn't touch her hair, but in the next shot her pony tail is perfect.
When Lorelai is talking to Luke about how to fix the oven, the 'Luke's' label on her coffee keeps moving.
When Richard hits Emily's car, you can see him walk from off screen towards her car, rather than coming from the door of his own car.
In a previous episode Rory comes to tell her dad to leave her mom alone because she's in a relationship and happy. When Christopher answers the door, he opens it outward. However, when Emily comes to talk to him at the end of this episode, Christopher opens the door inward.
Richard says that he and Emily will be renewing their vows on their 40th wedding anniversary. In Red Light on the Wedding Night (2001) Emily says that they have been married for 34 years. All the seasons are only a year. There is no way that it could have been 6 years between the beginning of season 2 and mid season 5.