Other mistake: Chandler tries to open the door that leads to his room, but Joey has sawed the door in half so only the upper half opens, and Chandler then falls over the bottom half. He has to hit it with some force to fall over it, but it doesn't budge an inch. (00:00:50)don_corleone
Other mistake: When Ross goes to see Guru Saj, he has his 'thing' removed. However, it is really obvious that Guru is not going anywhere near the thing, because you can see that Ross' shirt is still tucked into his trousers, and the Guru just rubs his hands along the shirt. (00:16:35)
Other mistake: When Phoebe makes fun of Ross' Princess Leia fantasy with the rolls, Rachel tries to stop her; the shots used are the same action, just from different angles. Look at Rachel's hands and the towel in her hand when Phoebe puts the rolls by her ears.