Legends of pacts with otherworldly entities which would ensure immortality to some hungry individual show up on countless planets. The cost always seemed so small until some trick of language or genealogical secret was revealed, but in the case of the eternal slimes of Sheltek, the curse was much subtler.

The unknowable machinations of evolution were the slime's demons, and their curse was eternal youth through periodic pubescence. To maximize progeny, evolution decided that the fittest of Sheltek ought to live forever, and it's solution was an excruciating transformation to revert the slimes to and from their childhood state. In adulthood the slimes accumulate calcium from their diet which is deposited in their outer membrane. Their calcified exterior restricts growth and encourages a smaller diet of nutrient-rich and fibrous plants.

Their increased density is similar to their larval form just before pupation, and with a premade cocoon of calcium, they go through their transformation to adulthood again and again until predation or disease kills them. Their initial pupation is painless, the numbing is built into their genes, but evolution is still working on numbing the successive puberties. Thus, the slimes feel themselves dissolve into their slimy adult forms, a process which occurs over days.