The concept is an old one that predates even the Heinlein novel, since it is central to the story "Pigs Is Pigs", which was very popular from its first publication in 1905 and beyond.
Bay of Pigs Invasion | Three Little Pigs | Disco Pigs | Bay of Pigs invasion | Bay of Pigs | Why We Love Dogs, Eat Pigs, and Wear Cows | Three Little Pigs (film) | Pigs in a Polka | Five Little Pigs | Top Jimmy & The Rhythm Pigs | Three Little Pigs (song) | The Three Pigs | The Silver Pigs | Pink Floyd pigs | Pigs Is Pigs | Pigs in Heaven | Peasants, Pigs & Astronauts | March of the Pigs | Front Porch Swingin' Liquor Pigs | Corky and the Juice Pigs | Amnesia: A Machine for Pigs |