User blog comment:Xilinoc/Ch. 567 (Rukia be like "I ain't even scared though")/@comment-5693502-20140205150657/@comment-1268838-20140205233538

The kicker here is that Rukia's ability is not "just" ice. As Nodt transmits his fear through whatever that substance is, which is undoubtedly composed of reishi. He could not comprehend that Rukia had lowered her body temperature to such an extremity.

As Nodt was just waxing philosophical when he was explaining fear to her. The fact that her ability happens to induce "death" is just irony.