A mortal threat in that they might be able to inflict some lethal wounds before being turned into red mist, also the alternative is to let Joe the mortal dodge just as well against a vampire with Celerity 4 as against another human and that is much,
much more problematic from a mechanical standpoint in WoD and in Dresdenverse alike since it makes super-speed far less useful against mortals, of which there are a lot more of them Exalts.
It should also be noted that a Circle of Exalts is a lot more powerful than the sum of its parts, it's almost midnight for me and I do not have time to write up an example so the best I can do is point you guys to
this channel of people including the creator of the supplement playing it (He's in City of the Bull God). They use the multiple action rules with each Dodge or Parry counting as its own action.
Anyway given the very late hour over here I'll talk more about this in the morning.
Good night guys.