In the one with the two parts (where Phoebe copes with her twin), the gang is in Monica and Rachel's apartment when Joey walks in and tells Chandler about Ursula at Riff's. In the first shot, you see Chandler unscrewing the cap off a bottle of water, but he doesnt take it off entirely. The view switches, and the cap is now off the bottle, nowhere to be seen, and Chandler's hand that was unscrewing the cap is now in his right pocket. The view switches back to the first view, and Chandler is still unscrewing the cap off of his water!