Actually, Ross and Monica Geller from the TV show "Friends" never had a pet dog. Perhaps you're referencing the episode where Ross reluctantly acquires a capuchin monkey named Marcel. Alternatively, there is an episode where Chandler and Joey take care of a dog named Clunkers for Rachel's colleague, but it's never stated that this dog belongs to Ross or Monica. It's understandable why some may think this, given the numerous episodes across the series where pets make an appearance or become part of the plot, however, none of those pets were a dog owned by Ross or Monica. If you need further information about animals and pets in the show "Friends," I'd be happy to help!