[Third Person POV],
When Andrew Dawn altered his offensive attack, the effects of his actions became immediately apparent since any mutant rats he hit began to fall 'dead' as their soul departed their body.
A living species' soul can be thought of as its identity, thus if it were to vanish, what would remain of that specie then?
Absolutely nothing.
The mutant rats that Andrew Dawn's soul magic spell left behind as "dead" were proof positive of this adage.
For one, they weren't actually dead; rather, their souls had been stripped from them, leaving them as empty, lifeless vessels. To be blunt, it was preferable to refer to all of these mutant rats as the living dead.
While they were still living, they were indistinguishable from the dead.