Continuity mistake: When Rachel says about her 6th date with Paulo, she is holding a decoration for the tree. In the next shot the decoration changes to a much larger object. Then, in the next shot, as she hands it to Monica, it has turned back to the original shape.
Continuity mistake: Just after Chandler explains the situation to Janice, she goes off crying, and Ross takes a photo. The flash is much brighter than it should be - the screen's whited out to disguise a jump cut - after the flash Chandler's noticeably further back than he was before.
Continuity mistake: When Ross say 'just a smidge' after Rachel says Paulo named her breasts, Phoebe is holding tinsel and Rachel is looking at Ross. In the next shot, Rachel is looking in the opposite direction and the tinsel has vanished from Phoebe's hands.