When Rachel and Chandler are out in the hall eating cheesecake off the floor, Chandler's piece is much closer to Rachel's piece than in the previous scene, when Rachel slapped it out of Chandler's hand closer to the apartment doorway.
Chandler walks in on Rachel eating the cheesecake, and the pen from the Magna Doodle on Joey's door is hanging down - but when the door is closed, it is back in its place.
After David leaves in the taxi and Joey is consoling Phoebe, Joey's coat collar repeatedly moves up and down several times between shots.
When Chandler says: "I am a horrible, horrible, horrible person.", Rachel is seen 'eating' the cheesecake at the edge of the shot. But she only dabs the spoon towards her open mouth before putting it back down, not actually taking in any food at all. A split second later, she speaks as though she is swallowing a large mouthful of cheesecake.
Aunt Millie inexplicably doesn't say hello to Monica at the wedding reception when she comes over to kiss Ross. However, it is plausible that Aunt Millie seems only to be fixated inappropriately on Ross. Also, Ross implies that Aunt Millie hasn't seen Monica since she lost all her weight, so maybe she simply didn't recognize Monica. Also, Monica states that their entire family was invited to the wedding, but we don't see them interacting with their parents. However, it's entirely plausible that Ross and Monica's parents simply couldn't attend the wedding.
David says that now he lives in Minsk, Russia, but Minsk is the capital of Belarus - which is a different country west of Russia.
It never occurs to Chandler and Rachel to simply order their own cheesecake, despite seeing the name and location of the bakery on the boxes of the original cheesecakes.