Chi-Chi

Chi-Chi was Monica and Ross Geller's dog when they were kids. Chi-Chi was first mentioned in season 1 episode 3, "The One With The Thumb", where Ross discovers Chi-Chi was not sent to the "Milners Farm" in Connecticut when in fact she died. In "The One In Massapequa", Monica mentions her in her speech during her parents' anniversary in an attempt to make them cry, however, this does not work as Monica's mother feels indifferent about the dog and Jack does not even remember her.

When Monica was a child she rode on her which caused the dog to need knee surgery at the expense of braces for Monica.

Trivia

Monica refers to Chi-Chi as both female and male.