Morphing into animals is very possible. Think about it, a human has 50% the same DNA as that of a banana and 99% the same as a monkey. What's left is less than 1% of 'humaness' that makes us all different and yet the same.
If it is possible to change the genetic coding of our DNA by some means by just a little, say 0.001% we could change into a completely new person. Obviously this wouldn't be instant and the cells would take time to change, so morphing would not be done in 5 seconds. If we extended this by let's say 5% we could change into an awful lot of different species, of course the problem of changing back arises.
With new Stem Cell research it is possible to manipulate cells and heal the body, effectively regenerating the section affected. This is on a small scale, however, and doesn't take 5 seconds. As said, how would we change back? It is easy enough to change into something else by manipulating the DNA and placing it in our bodies but unless we developed a time mechanism we would be stuck as the animal for ever.
Another problem is how would we change all our DNA in all our cells in order to change, we would need to keep the brain as it is in order to think like a human but that brings more problems, what if we changed into a bird? How would our brain know how to fly? Maybe it would know already as after all we only use 6-7% of its' full power at this time. Imagine what would happen if we used 100% of our brain power, apart from us exploding we could harness enough power to manipulate time, space, particles, the list is endless!
Stem Cells have all genes switched on and if we could somehow create animal cells inside our own bodies by maybe using radiation of something similar it would be possible for us to change. The problem is adverse affects and we don't know exactly what genes radiation changes and affects, in fact we don't even know what most of the genes we have do! So what hope to do we have of morphing until we understand what every gene does and how radiation exactly affects a cell's DNA.
Morphing is possible once we have done enough research, much of today's research fits into the idea of morphing and we could use a lot of it when we decide it is time to experiement. Morphing into animals or developing their traits would be stage one or the last stage, it may even be possible to effectively become immortal; whereby if we are injured we regenerate new cells, like in Doctor Who.