User blog comment:Xilinoc/Ch. 567 (Rukia be like "I ain't even scared though")/@comment-1489595-20140205190619/@comment-11051098-20140207154457

Rukia states in the chapter that she brought her body to a temperature below zero, making every molecule in her body stop, and Äs' fear was blocked on the surface of her hand. It seems the explanation is as simple as that - she froze her body so that his fear could not enter it.

Sorry for writing what's clearly stated - and obvious - in the chapter, but I want to point it out.