I thought I would explain what a "Therian" is to people who do not know what it is or to those who see it as attention seeking Fluffies.
A Therian is a person who has the spirit or soul of a particular animal (an existing animal by the way) Having this spirit does not grant you special powers it does not make you better than anyone else and a Therian is a human just like everyone else. Some beliefs are that someone has connected to the animal side of themselves that everyone has and you just need to be awakened. The first one is my belief (also the most common but I don't dismiss the second)
Therianthropy is purely a spiritual thing as you all know you cannot break the laws of physics and cannot shapeshift. However types of shifting do exist but they are not physical. A P-Shift is a Phantom shift not Physical; this is were a Therian feels they have the wings/tail/paws/claws/scales of their Therotype, no one can see it or feel it apart from the Therian those parts belong to.
An M-Shift is a Mental shift where one takes on the Mentality of their animal, walking on all fours growling, basically acting like their Therotype.
And the S-Shift, Sensual shift; having similar senses to the animal better eyesight/hearing ect or worse depending on the animal. (I myself have these often)
There are other kinds of shifts but these are the most common.
If someone is claiming a Physical shift then by all means label them a fluff, as you know it is not possible.
If anything Therianthropy is more like a knowledge of yourself than anything else like your past lives.
Therianthropy along with the Berserkergangr along with certain illnesses are probably the orgin of the modern werewolf myths.
For more information on Therians and Otherkins follow these links