How I Believe A Physical Shift HappensI think that this is what really happens when you shift. (I dont know 100%, this is a theory though)
First off, your DNA actually doesnt become the DNA of a wolf. This would mean that you would have to have it already, which in my opinion is sorta hard to...obtain, and it would leave you with the mindset of one, which you wouldnt be able to shift back from. So your body turns on certain genes to make you identical to a wolf-the reason you are able to keep your human intelligence at all. But since all the creatures of this planet share identical DNA, it means that you already have the genes like one, but they need to be arranged more wolf like (or whatever animal you may be.) This is how an M-shift is obtained in the first place (your DNA has certain wolf like genes turned on. For example, both wolves and humans shair the genes that determines hair growth and hair density. If you were to keep the gene turned on longer in humans you would have a human with a lot of long hair everywhere instead of it on the head only. Which explains why it's harder for bird and reptilian therians to shift, since it's takes more genes being turned on and off to get the same look that the animals have.
When shifting muscle, the fibers expand or contract simutaneously ba
Note: You can shift into a creature of any size, as long as you have enough matter to accompany the shift. You could shift into a 30 foot snake or a 50 pound dragon, as long as you have enough matter to make your body, or else you'll come up too short (or too big.)
In other words, when you M or P shift, you're actually making a body out of your own genes that's like a look alike of the actual animal's body using the instincts and genes that you have. This also would explain otherkin and weres well, since they wouldnt exactly need a living animal to shift into-they're shifting into thier own created body ba
Many people seem to think the most unbelieveable part of physical shifting is the brain. They tent to think that, since the brain is a delicate organ, changing it's size or shape would hurt the user, and leave them mentally disabled, if not worse.
But I believe I have found a way for this to happen without any of the problems most people tend to describe. It's very simple: say you're shifting into a wolf or housecat. Even though you will remain about the same in size, the skull will be smaller. Now, my theory is that you dont lose any mental capabilites, nor info, because of how the brain compacts itself during shifting. Your brain, as a human, is very wrinkley (lol) and those wrinkles are part of the reason we can think the way we can. But when you shift, the brain compacts, so more brain cells press in closer together, and your brain gets more wrinkely, so to speak. You lose no brain mass, and your brain is still intact, it just gets compacted. Think of it like a rag in a container. As a human, you have the rag (your brain) spread out inside the container. It fits perfectly, with just enough room to not touch any of the sides (like how your brain doesnt touch your skull.) But say the container gets smaller. All you need to do is fold the rag up, and it'll be another comfortable fit. No piece of rag is cut out, and nothing is lost, so if you return to the bigger container, the rag can just unfold, no harm done.
I hope this helped ^^