Another way of looking at the whole aspect idea - is that in various mythologies - some goddesses, that may be representative of the Slayer (like Durga, & Kali (Hindu), Athena (Greek), Neith, & Bast(Egyptian)).

These warrior goddesses' also often have animals that accompany them.

Durga - Lion or Tiger(i.e. Big Cats/Panthers), Kali - a dog or jackel (Canine). Athena is found with an Owl (Raptor/Bird of Prey). Neith with a cobra or crocodile(Serpent), and Bast with a Cat(Feline).

So the aspect could be representative of both the slayer's actual spirit guide, as well as the goddess that often accompanies that animal. As a result - maybe the personality in each aspect may be more reflective of the goddess than the actual animal.