User blog comment:Xilinoc/Ch. 593 - Marching Out the ZOMBIES 4/@comment-24572618-20140820220922/@comment-1268838-20140820232156

I don't get the impression that Gigi manually manipulates her zombies. She gives them an order, and they follow it to the best of their ability. This is why a zombie like Hitsugaya, who is not actually dead, is particularly invaluable. Under the effect of the drug, he can still attempt to follow Gigi's "kill" order, but that would only cause him to loop again... I think Mayuri might be conditioning him to break out of Gigi's control, since he was able to confirm that Hitsugaya has semblance of personality intact.

As for freezing Mayuri solid without killing him, I can only guess that he can't for the above reason - he was essentially ordered to "kill." Which makes me wonder what these events look like to the outside observer.