No worries! Grimer is a thoughtful Pokémon - in its own mind, at least. It's noticed that, aside from some parts of Union that currently resemble the Old City (being utterly destroyed and looking like ruins), humans place a great deal of value on keeping their living areas clean. This does not seem healthy to Grimer, so it enjoys tracking slime across clean floors/tables/what have you, and then expecting to be praised. It's like a muddy puppy dog.

Made of sludge.