It was widely publicized that Kudrow was afraid of the duck who made an appearance in season three. Before that, Ross had a pet monkey, Marcel, who was actually played by two monkeys: Monkey and Katie. Marcel was written out of the show in season two because it became too time-consuming to shoot scenes with a monkey. According to Katie’s trainer, Nerissa Politzer, Monkey was once supposed to pick up a bra, but ended up throwing it at Aniston instead. There’s a fun blooper (at about the 6:20 mark above) in which Rachel is trying to explain a TV show to Marcel, but it doesn’t go so well.