The One with Mrs. Bing - S1-E11
Continuity mistake: While everyone's at the restaurant Rachel dips a tortilla chip into guacamole and gets some on her hand. When Paolo takes a bite from the chip he also eats the guacamole off Rachel's hand while she's still holding the rest of the tortilla chip, but in the next closeup Rachel's hand is empty, then in the next shot the remaining tortilla chip reappears in Rachel's hand. (00:06:45)