At 5:19 we can see Ross writing on Magna Doodle "Joey enjoys the" when Rachel enters. At 6:02 when Emily enters, Magna Doodle still reads the same but at 6:06 it reads "Joey eats little V".
When Joey is talking to Rachel about taking her bra off a-la Flashdance (1983), the number of bites in his sandwich changes between shots.
When Rachel is talking to Joshua near the drinks table at the party, he is holding a blue cup in his left hand and nothing in his right (this is most obvious when she's offering him a cherry). When she begins to choke, he raises his empty right hand to pat her on the back, then when she walks away there is suddenly a bottle in his raised hand. The shot changes, and his hand is again empty and he reaches down to the table and picks up the same bottle.
When Joshua and Rachel (who is trying to take off her bra without taking off her shirt) are talking in the bedroom and he finally confesses that he's interested in her, the amount of her bra appearing from her sleeve changes from shot to shot without her working on it.