It was once believed that whenever a grass pokemon died, it became a Carnivine, and that other ghosts are the spirits of the animal kingdom. But despite their levitation and thin, wispy bodies, Carnivine are not true ghosts, but living, floating plants. Their enormous, toothy mouths are used not on humans, despite the primal terror they evoke, but solely devour those spirits, such as Gastly and Yamask, who are unable to move on from this world.
For this reason, the Carnivine are often used to perform exorcisms, although never without ethical controversy. When a traditional exorcist convinces a ghost to move on, it fades into nothingness. But when a Carnivine hunts them, the ghost will attempt to flee, be chased through walls, and scream in haunting, abject terror before being eaten. Some have taken this fear to mean that Carnivine gain their nutrients not from the ethereal, typically gaseous bodies of ghost pokemon, but by eating – and destroying – their very souls. But death itself is a painful process, whether oblivion, reincarnation, or an afterlife awaits, and this is as true for those who have suffered it yet are bound to this world as for those who have not yet died.
Interestingly, no one has yet figured out how to kill a Carnivine. Darkness does not make them wilt, nor does keeping them away from ghosts for prolonged periods of time make them starve to death. It is possible that these pokemon, like many grass-types, are extremely resilient and long-lived, and that it is simple coincidence that none have yet seen them die. But some consider them true immortals, for they are already halfway in the spirit world, and believe that death is conquered not by becoming a ghost, but only by discovering some way to become a Carnivine.