When someone befriends an animal, s/he obtains the ability to unite their souls together and take on the form of that animal as well as its abilities. S/he also gain some properties of that animal even when they are no keener t transformed, such as resistence to cold or senses. If s/he really wants to s/he can half transforms taking on characteristics of the animal and their normal form
As they travel they notice a horrible rotten smell. As they travel it gets stronger and stronger forcing them to cover their noses and mouth less they choke on the horrible smell. Rotting animal carcass that has been ripped apart and tracks all over, covered in maggots.