Lwcwm is the most alien in behavior of all of the creatures living in the Mongleys' drain. (Jag Tallerson, the head of the family of drain denizens, says that while he does consider Lwcwm part of the family, Lwcwm is adopted.) Lwcwm can speak intelligibly through vibrations of the spines and legs, but it's not clear how Lwcwm sees given the absence of obvious eyes, or sustains itself given the absence of any obvious orifices through which nutrients can be taken in, or performs a number of other basic bodily functions. Lwcwm is not unwilling to answer questions about these matters, but the answers often do little to clear things up; while Lwcwm's speech consists of recognizable words put together in grammatically coherent ways, the sentences still don't often seem to make much sense.
Lwcwm doesn't seem to have or identify with a fixed gender, and Lwcwm's preferred pronouns vary from day to day, subject to Lwcwm's pronouncements of "Today I am he" or "Today I am she." Lwcwm doesn't limit him/her/itself to conventional third person pronouns, however, and the times when Lwcwm proclaims that "Today I am you" or "Today I am I" may lead to some confusion.