Eren blows a lock of hair out of his eyes and only grumbles a little when it flops limply back to his face.

His hair is

greasy.

He hadn 't known his hair could be anything

but

greasy until his humans took him in and showed him such innovations as soap and warm baths. Even then, he was still in a daze of cataloging all of the differences in his human-shaped form to truly appreciate such minor differences until later.

Were he back in the endless expanse outside the Walls, he would have scrubbed his scalp in a lake or river to wash out the grime, but he doesn 't know if there 's one close to here. He probably

could

wander around to find one, but he doubts that the soldiers guarding him would like that very much.