User blog comment:IamJakuhoRaikoben/Chapter 388: Erza vs. Minerva, Review./@comment-5598380-20140613133747/@comment-7418318-20140613161057

They did crawl out of the liquified, frozen and re-liquified walls and ceilings, so getting a bit dirty is only to be expected. Not to mention that they fought the small-fry on undercube (as a close-combatant Gajeel is boud to get a bit dirty while fighting) and likely also patrols in the rest of cube, like the one Natsu and Lisanna ran into further inside.