Sanji had a habit of falling with his butt facing up, and it was unknown why. Until Zoro, tired of tripping over Sanji. Ends up hitting Sanji on the ass and shouting: "Quit moping, idiot cook!! You're blocking the fucking way!!!" After this speech from Zoro and the slap on the ass. Sanji ended up moaning loudly in response.

Zoro was shocked by the way Sanji reacted to the slap on the butt and just remained silent.

It was as if a secret in Sanji's body was unlocked... Those moans, Zoro wanted to hear more.