It's early on that Zoro falls a little bit in love with his laughter. Before he understands who or what Luffy is, really. It happens without his knowledge or consent, because while that beaming smile of his is enough to make you follow him into danger and madness, it's the laughter that really steals your heart.
(He stole his heart, his dream, his soul and Zoro didn't even notice)
Only when it falls silent for a while, when the Captain's duty weighs heavy and Usopp leaves them, does it grow clear to Zoro just how much it is worth to him. To simply hear this laughter. That's how he can stay strict about their young comrades return, for he can't bear to see Luffy suffer again. Which he will, if the crew falls apart the next time the stress of the journey bears too down heavily on them all.
When they sail away, when the smile is fake and the laughter muddled, he almost relents – take the fool back, let's all capsize the ship and throw us over the end, just don't lose your joy!
But Usopp finally proves to be the man he's dreamt to be, just before it's too late. He lays down his pride and throws away his wrongly aimed hurt over their Merry's death and Zoro feels his own smile grow painfully bright when he sees the two friends reunite.
(He stole his hopes, his future, his honor and glory and will, and Zoro didn't even care)
Because Brook's music resonates perfectly with Luffy's laughter, he can welcome the skeleton aboard as soon as he wakes up. Old, crazy, monstrous... but his laughter is true, his fiddle plays only tunes of joy. Zoro feels rare tears attempt to get free, when he sees his Captain dance to the tune he vaguely remember from his feverish sleep, and he knows they have found the right musician.
Later, on the dark island, the bell tolls. Heavy, dark, each note proclaiming the death of a dream.
But in Zoro's ears, silver bells are chiming. For his Captain is alive and waiting for him, and no heartbreak, no pain, can silence his laughter. Even beneath this starless sky, he can still feel its echo in his heart and his own smiles grow more common, as the months pass by and the reunion of the crew nears.
(His loyalty, his dream, his devotion and love... Luffy never had to steal anything at all. He gave it away freely and wants nothing more than keep giving until the end of their days).