"Dr. Beagle and Mangy Hide" is an episode of Season 3 of All Dogs Go To Heaven: The Series.
Charlie, intending to try a brand of dog food called Happy Hound, does, only because it was tainted with a mutation chemical (thanks to Carface and Killer), he turns into a monster.
Eventually, after Itchy has saved Charlie, the latter never wants to have anything to do with Happy Hound, not even to see it. So when Sasha apologizes to him for not believing the events, brings it out, and offers it, Charlie knocks it off her paws, to so much fury of Sasha that she ejects him.
Not only is the episode's title a parody of Jules Verne's short story "Strange Case of Dr. Jekyll and Mr. Hyde," so is part of the storyline itself.