Why do animals who live underground appear always clean and not full of dirt? (e.g. worms, mice, rabbit)

Question

Why do animals who live underground appear always clean and not full of dirt? (e.g. worms, mice, rabbit)

In: 7599

Answer 1

Because if dirt clung to them, obviously it would be harder to crawl through dirt, so they evolved to be able to move through it with less friction.