Whistle While Your Wife Works - S5-E5
Other mistake: When the guard is turning the vault handle, the handle doesn't move, but the guard's arms do.
Airport '07 - S5-E12
Other mistake: As Quagmire sits at the bar, Hugh Hefner comes and gives him a pep talk. During it, he says John Holmes said Glen Quagmire is the best pilot. Unless he had seen the news or knew him personally, Hefner couldn't have called Quagmire by name.
Boys Do Cry - S5-E15
Other mistake: Towards the very end, they automatically head to the car, planning to leave Texas, without any of their items from the house packed in the car after running away from the mob at the Miss Pageant Contest.
Other mistake: Peter goes back in time and sees Lois at age 18. Death says everyone will see Peter as being 18 too. Problem: Lois and Peter aren't the same age. In later episodes, Lois reveals she's 2 years older than Peter so Peter should be 16 when he meets Lois.
Blue Harvest - S6-E1
Other mistake: In the scene where the Millennium Falcon has just left the death star after Obi-Wan has been killed, there are two shots of the ship flying away through space. In the second shot, the cockpit is missing. (00:33:35)
Other mistake: Joe Swanson is colored incorrectly. His color scheme is apparently the same as Peter Griffin's when looking at his skin color and hair. It is fixed shortly afterwards. (00:11:54)
The Man with Two Brians - S7-E5
Other mistake: Brian puts in a video tape of him as a puppy. But he hasn't been with the Griffins since he was a puppy. Peter picked him up from the street as a homeless adult dog.
Tales of a Third Grade Nothing - S7-E6
Other mistake: In the cutaway at Ford's Theater, Abraham Lincoln receives a cell phone call from someone who is implied to be Thomas Jefferson. While the anachronism of a cell phone in the Civil War can be ignored as humorously deliberate, Lincoln can't be talking to Jefferson; by April of 1865, when Lincoln was assassinated, Jefferson had been dead for nearly 40 years.
Suggested correction: Where are you getting the implication that it is Thomas Jefferson? You seem to have misunderstood the joke. "I hear you took that black chick home. You're welcome." is not a reference to Jefferson sleeping with one of his slaves. It's simply a reference to Lincoln freeing the slaves. Tom is just a generic name. (Besides, if you're complaining about historical anachronisms in Family Guy cutaways, you're probably missing the point.)
Road to the Multiverse - S8-E1
Other mistake: In every universe - except for the double-headed universe - Brian and Stewie travel to, they (seem to) replace the version of themselves that universe already has of them, but then in the Dog universe they have a separate version of themselves that they continuously interact with.
Other mistake: A bank wouldn't lock someone in the vault all night. Employees make sure customers have left before locking up for the day.
Other mistake: Joe salutes Quagmire's Dad. His legs are paralyzed, yet he uses them to push himself backward in his wheelchair.
And Then There Were Fewer - S9-E1
Other mistake: As Joe is driving up to the house, just before coming to a complete stop, you can see that his window is completely closed. After stopping, Peter says "Joe?" Joe says "Peter?" Joe's window is now fully open. Trouble is, Joe seems to be completely surprised by Peter standing there which implies he never saw Peter even after stopping. His window has mysteriously opened immediately. (00:04:05)
And Then There Were Fewer - S9-E1
Other mistake: When everyone is in the dining room after James Woods was killed, Derek and Jillian can be seen hugging each other a little bit, and Derek's left arm is missing.
And Then There Were Fewer - S9-E1
Other mistake: When everyone is leaving the mansion after Stephanie was killed, 3 mistakes happen at the same time: Dr. Hartman came alone, but there is a person sitting in the front seat next to him. Derek is in the car he and Jillian came in when they got here, but he is alone. And Carl was getting into Herbert's Ice Cream Truck, which was in front of his own truck.
And Then There Were Fewer - S9-E1
Other mistake: When they are chasing Tom around the dining table, they huddle up in a circle. Everyone is looking at Peter talk, and when Doctor Hartman says "Damn, that is awfully risky," if you look at Carl's eyes, they clip outside their eyes to look at Hartman.
Road to the North Pole - S9-E7
Other mistake: Cleveland's house, across the street from the Griffins, is absent in the opening overhead shot. Then the scene changes to inside, and we can see his house through the window.
Screams of Silence: The Story of Brenda Q - S10-E3
Other mistake: This episode is the only one in the entire series where there's a peephole in the door.
Stewie Goes for a Drive - S10-E4
Other mistake: Stewie is standing up on the driver's seat yet he can drive a car normally. His feet don't touch the pedals so how is the car moving?
Other mistake: When Stewie and Brian are in Stewie's bedroom in the future, Stewie's time machine is nowhere to be seen. (00:15:00)
Other mistake: When Peter was rescuing the Fishmans he totally missed grabbing the woman's hand but she didn't fall. (00:19:50)
