He had either undressed or caused his own clothes to go away - probably the former she decided; Mike found buying clothes for himself without interest.  He still could see no possible reason for clothes other than for simple protection against the elements, a weakness he did not share.  They got into the tub facing each other; she scooped up a handful of water, touched it to her lips, offered it to him. It was not necessary to speak, nor was the ritual necessary; it simply pleased Jill to remind them both of something for which no reminder could ever be necessary, through all eternity.