An event called the Jellicle Ball was referenced by Eliot in the poem "The Song of the Jellicles", while a cat version of heaven known as the Heaviside Layer was mentioned in one of his unpublished poems. Nunn expanded on these concepts by conceiving the Jellicle Ball as an annual ritual in which the cats vie to be chosen to ascend to the Heaviside Layer, thus giving the characters a reason to gather and sing about themselves in the musical. He also added the element of rebirth as a play on the idea that cats have nine lives.