Zoro is a cambion, which means he feeds on sexual energy. A small crew like the Strawhats, its not normally enough to keep a cambion satisfied, but Sanji happens to be an abnormally sexually driven cook so it usually works out okay for Zoro. At least, it works out alright until Sanji finds out that Zoro's been taking energy from him through his dreams. For Sanji, he's trying to wade through the confusing mess of emotions for a certain marimo after a surprise kiss on the battle feild. It's not easy to do on a normal basis. It certainly isn't any easier when the man he has deeper feelings for is a cambion. Then everyone learns how important it is to keep their local cambion fed, for if they don't, someone might get eaten. literally.

It’s like a high when the both of them resonate on that same frequency—two radios spitting static at each other ninety-percent of the time until they find overlap for one, just one, perfectly-played song. The music is brilliant and vibrant when it’s playing. It’s always over faster than Sanji ever wants it to be.

Three inches in front of Sanji's face, Zoro is wearing an expression that could wither stone. "What the fuck," the swordsman snarls, "do you think you’re doing." The remaining logical dregs of Sanji's brain recognize that he's just gotten himself into a pretty dicey situation. The rest of it apparently doesn't fucking care, though, because the absurd line of response he comes up with is to grin right in Zoro's supremely pissed-off face and say- "Well, what was your dumb ass doing?" In which the crew’s plastered, Zoro needs to blow off some steam, and Sanji gets taught a lesson or two.