Zoro was napping quite contentedly on the deck of the Going Merry, as he had the tendency to do every afternoon. His arms folded behind his head, shirt draped over the dumb-bell on the deck a few feet away from him.
Sanji watched through the window of the galley, a look of curiosity on his face. In one hand he held a knife, in the other he held the fruit he'd been cutting for Nami's afternoon snack. His hands were still now, his entire attention focussed on the swordsman.
His chest rose and fell softly in the rhythmic pattern of sleep and Sanji felt his own breathing settle into the same pattern. A breeze blew gently across the deck and as Sanji watched Zoro's foot twitched slightly as it blew across his stomach.
Sanji let go of the knife with a slight clatter and walked out of the galley and over to where Zoro was lying. With only a slight pause he dropped to the deck beside him, still watching.
He was fairly certain that the swordsman had woken up as soon as Sanji had gotten within attacking distance, but Zoro showed no change outwardly.
Sanji studied the swordsman silently for a moment before he reached out and ran his fingertips lightly over Zoro's stomach, barely touching the skin.
The reaction was instantaneous. Zoro's eyes snapped open, focusing on Sanji's, every muscle in his body tensing. Sanji continued to run his fingers over Zoro's abs, feeling them quiver slightly under the touch.
Sanji hummed lightly, in the back of his throat as he slowly flattened his hand out so that his palm was flat on Zoro's stomach as he rubbed it.
Zoro's leg twitched slightly as Sanji's hand brushed the top of his pants. A smile, small enough that it was liable to be counted as imagined, tugged at Sanji's lips. Zoro had apparently forgotten how to breathe.
Sanji brushed the top of Zoro's pants again and Zoro's leg jerked more noticeably this time. Sanji's smile widened into what could actually be called a smirk. Zoro still couldn't breathe.
Then Sanji abruptly stood and dusted off the seat of his pants.
Zoro's sucked in a breath, "What the hell?"
Sanji shrugged, "Just curious."
And with that, Sanji walked off. Zoro sat up, watching him until he entered the galley. Then he stood as well, "'Just curious' my ass," he growled, following him into the galley.