It's not necessary for Yuugi to check on Seto, as it turns out. Eventually, he exits the bathroom of his own accord, standing unsteadily on two legs. If his tail wasn't out, he would surely have fallen over by now, but he ought to walk like a human, if he's taking a human form.

"Have you any garments? Humans don't like to be solely in their own sc...skin, do they?"

He almost says scales. But humans do not have scales.

When Yuugi turns to look, he'll find that the dragon's holding the bowl before him. He's eaten the entirety of the contents, and there's a tiny grain of rice at the corner of his lips.