When Brian, Meg, Stewie, and Chris are running down the basement steps, some of Brian's head gets chopped off.
After the Twinkee the Kid flashback the scratch on Peter's nose keeps disappearing and reappearing.
The brown mouse traps that Meg set down around Joe in one scene, shift positions and change to grey in another scene.
When Meg enters the scene to set the mouse traps around Joe, she just suddenly appears, being a few frames out of synch. This is repeated when the family walks away from New Quahog.
When Peter takes Chris' tree to the backyard to shoot it, we can see Joe's driveway in the background. No one is shown in the background, but a few minutes later we see that Joe is melted into his driveway even though he was not there when Peter walked past.
When they say goodbye to their home, the screen stutters a little between the words "Well" and "goodbye sweet home".