Kaiba lets out an annoyed tsk that really represents the only sound he can make, since it's just clicking his tongue. Then slowly, he tries to sit up, which is somewhat of a mistake, as evidenced by his wincing.

No, he's going to keep a straight face. He's not going to let any of this get to him.

(he remembers dying. he remembers laughing until he drowned in his own blood, staring at the ceiling with an unhinged expression)

Not again. He won't.

Slowly, silently, he nods.