As soon as Yuugi says that, Kaiba pulls his hand back. It's uncharacteristic for him to look so out of his element, but Yuugi has that effect on him.

"Don't say such foolish things," he mutters, "Not when we're like this. It's not some romance novel you're in, just in case you haven't realized."

And at that point, Kaiba sits up, pulling one knee up so that Yuugi can't see how he's reacted to all of it. To his blood...to the sensation of biting a human for the first time...

It's his shame.