As mentioned in Sponge Balls, Frances Marshall credits these to Jack Strothers. However, in Magic Manuscript, Sept./Oct. 1986, p. 39, Charles Reynolds claims that Carlo (Sommer) invented the idea behind the Multiplying Sponge Rabbits, by marketing a trick in 1930 called “The Gopher Birds”. Bob Nelson is commonly credited with the later sponge-rabbit variation, which he marketed as “Peter Rabbit Goes to Town”.