Technically speaking, a person can't gain mass spontaneously, so is there anyway it's plausible for a man to transform into a larger animal? I'm writing a paranormal fiction series with vampires and were-creatures and such, but I want into to be more in the realm of scientific rather than magical. Of course, I'm aware that most of it will really push the limits of what's actually scientifically possible. However, I want something that can at least be believable. Similar to how we know modern day zombies could never happen due to a number of complicated reasons if you really delve into the science, but in the realm of the story it's credible. Thank you in advance!