>>33755565In-universe it is a bunch of rocks with minimal to no organic material, seeing as how it's in the Mineral egg group and no other.
Its behavior seems reminiscent of the common earthworm, seeing as how it just digs and is non-carnivorous.
The Pokedex calls it a Rock Snake, but the Pokedex calls stuff a lot of things they aren't exactly based on.
Its head is vaguely reptilian. In RGBY many Pokemon were given reptilian traits for a "cool" factor, such as Scyther and Golem.