Continuity mistake: when Monica is asking Zack if he or any of his blood relatives has diabetes, Zack's cutlery changes position twice. In the shot facing him he has his fork in his left hand and his knife in his right. When it changes to a side shot, he is gesturing and doesn't have anything in his hands, without having time to put the cutlery down. Then when it cuts back to a front shot, he picks up his fork, which is now on his right, and starts eating.
Continuity mistake: Ross is on about going to Maryangela's to Chandler. He picks his drink up, the camera cuts and he picks it up again.