Sanji would admit he liked Zoro's fighting style at night. This confession caused quite the stir. He played it off by saying, at night it was dark and he couldn't see the stupid moss head, it was a relief. Which immediately started a fight between the two.
But as he watches the swordsman from the kitchen window, he knows the real reason. The way the moonlight reflected off Zoro's blades as he swung them was hypnotizing. Like they were dancing around him in a protective waltz.
Sanji blew out a puff of a smoke as he exited on to the Sunny's deck. Zoro held one sword up to the silver light examining it. The blonde sighed, remembering the first time he felt jealous over Zoro's precious Wado, how he wished Zoro would look at him like that. He scoffed. He had to be losing his mind.
Zoro looked up at him curiously. "What is it cook?"
"Nothing, just came out to enjoy the moonlight."