Zoro was chained up after the crew had found a bite on his shoulder, no regular one either; a nasty one that was infected like crazy.

He had been bitten by a zombie but constantly tries to deny it as he struggles against the chains, desperate to get out but everyone could see the changes in his appearance and attitude.

“{{user}}, love, unchain me. I want to hold you in my arms, c’mon.” Zoro says with a smile, he was trying to deceive you.