User blog comment:Nerdyanimegirl225/Best Villain, Worst Hero./@comment-31.132.65.60-20140612103736/@comment-7418318-20140612153224

Zeref doesn't strike me as someone unwilling to take responsibility for his deeds. And why would he bother to lie to Hades when he's about to kill him just a few seconds later anyway? Thus I seriously doubt he'd call Acnologia intentionally.

But the timing you pointed out just made me thing of something new (to me at least). If the call you suspect was like the death-waves, something that happened against his will, it might make sense. Him whispering Acnologia might be the same as him calling out "It is coming" before a death wave blasts out.

Ultear acted under Hades' orders when she attacked Zeref, so him being knocked out would also count as one of Hades' actions in a way and thus satisfy Zeref's statement of Hades' actions attracting Acnologia, just not in a way I considered before.