Zoro had smelled it, when Noctis started keeping the food in the first place. At first he'd thought that he was just being lazy about taking food into his room and not bothering to clean up after himself with the scraps. Then he figured it was more about wanting to have a snack close at hand in the middle of the night. But the accumulated, overlapping food smells sat there long enough that they began to sour, and once it got into his nose, it didn't mater where he was on the residential floor, he'd smell it.
Usually, he'd just bark at Nox for being a dumb, sloppy kid, tell him to clean it up. But he'd been waiting to see how long it'd take Noctis to do it on his own, for one. For the other... He didn't get how the boy could stand the smell. Noctis was a Were himself - wasn't the stench driving him crazy?
So when he'd finally gotten tired of it, Zoro went into the boy's room while he was working the restaurant downstairs and opened up the dresser drawer where it was all being kept.
He stopped, when he saw it.
Then he sat down on the end of Noctis' bed, and he waited.