Ah yes! You can store the whole human body in a cavity of the cat's body, and vice-versa; lightspeed is no issue - indeed you could run the whole thing at ordinary neural speed. This might even solve the problem of how to order a cat's body around; the Animagus in effect has a cat as an ordinary part of her body, and has learned to operate it the same way she learned to operate her human body.

One problem is the carrying-over of wounds from the animal to the human body, and vice-versa; this does not seem implied by the model, and requires additional explanation. Psycho-somatic damage? Since there a requirement for conscious control of which shape one is in, the opportunities for unconscious failure seem strong.