After Lily takes off her engagement ring to try and attract a pass, she is seen talking to Robin wearing her ring. It then disappears when the gay guy comes up to tell her she sat on a grape and she pulls it out of her pocket to show him.
Marshal states that he's never been in a fight before but later on we learn this to be untrue. He often fought with his brothers growing up.
After Ted and Barney are released from TSA, they call Marshall to tell him plans. Marshall has to do a U-Turn three times, but instead of turning the wheel left three times, he turns left, right, left. Right turns would go off-road.
When Barney and Ted are flying to Philadelphia, Ted calls Marshall while flying. However this is impossible since you cannot use your cell phone while in the sky, there are no cell towers.
The plane shown taking Ted and Barney to Philadelphia is a 747, but the inside is of a much smaller aircraft. Also, no airline would use such a large aircraft for such a short route.
While Barney and Ted are in the taxi en-route to the airport/liberty bell you can clearly see the New York State registration and safety inspection on the drivers side of the windshield.
Marshall messes up his U-Turn.
Near the end of this episode Marshall comes into the bar and is saying that he is going to fight the gay guy, and then the guy tells him he's gay, and Marshall says he has never been in a fight before. But in episode
4.10 - The Fight, Marshall says he's been in plenty of fights.