The pretty blue light faded and went out, and the shrieking hum faded into a cold silence. Slowly, the former human opened his eyes and looked around. Looking down he could see human flesh, but below it, finally, thank god, his body changed from pale pink flesh into chestnut brown fur that ended in black hooves. Still not daring to believe he spun his head and waist around and looked down upon his barrel, the body of a horse, his body, all stretching out behind him, furred, expanding and contracting with each breath, standing on four legs, ending in a tail. It had worked! Smiling, grinning, he stood up on his hind hooves and made his way out to celebrate.

A fairly typical, though badly researched post transformation scene. Personally, I don't worry about the blue light, the humming machine, or the pseudo-physics behind the transformation. They're a free gift to the writer. I've 'suspended my disbelief' to accept the transformation. But then I read on, and lose the illusion. There are two things here -- first, hooves are not black. Pale, grayish, but not black, at least not naturally. But, it is a centaur, I can forgive that, but at this point I'm starting to be wary. I've lost my immersion in the story and rather than experiencing it, I'm reading it. I'm now one level removed. Then we have the centaur stand up on his hind hooves and walk out. At that point I just stop. It's obvious to me that this person has no clue as to what they're talking about. A centaur could rear up, but the body isn't structured to allow extended movement on only the two hind legs. At this point I have to ask myself what possible benefit is there to continuing to read? Anything I read won't teach me anything, won't enable me to imagine the experience because I already know of two flaws. All I'm left with is a desperate hope that maybe I can recapture the perceived reality of the story. Likely I won't.

Okay, admittedly the 'walking on hind hooves' was kind of an extreme example. Probably just about everybody knows that horses move around on all fours. The black hooves are a more subtle and common problem though. So, how can a writer keep this from happening? As you've probably guessed, the answer is research. In this modern world it doesn't take long to search the internet, find some pictures of horses, and make use of them. It's not hard to find out that a horse walks, trots, canters, and then gallops, or the hoof patterns of each of these methods of movement. For a reader who has no knowledge of horses, screwing up these patterns won't mean anything -- they won't know any better. But if somebody knows horses and reads about how your centaur 'accelerates from a canter to a walk' then they're likely going to stop reading and not read anything else you write. Five minutes of research can prevent this.

The same applies even for non-transformational fiction. How much fantasy have you read that had water flow up hill, the sun slowly fade out like somebody twisting a dimmer switch, and the oceans tasting like chocolate milk? Probably none. The reason is that the more realistic the story reads, the more research the writer has done into other things, the more that you, as a reader, are willing to accept that magic works. That more that you, as a reader, are willing to enter that 'suspension of disbelief'.

So fine, a writer has to research basic things, or abstract if they're too lazy to find out. Instead of describing the color of a centaur's hooves, just don't mention any colour; instead of describing canters and trots and gallops, just say that the centaur 'moved slowly' and 'moved quickly'. Yes, you can brush over the problem, but your story won't be as good, and the reader will find it harder and harder to feel and visualize the scene because of the lack of concrete description. But yes, you can do that. And you lose even more.

Researching facts almost always provides more information. Everything is interrelated. Finding out one fact almost always gives you other facts, and those other facts can give you a completely new idea to incorporate into your story. Some examples from my own experience. Writing about centaurs I researched horses, and learned things such as the fact that there are horseshoes made primarily of rubber for use on streets; and that there are what in essence are 'rubber boots' for horses. I learned that wild horses tend to have larger hooves than domestic breeds, and that the hoof acts a bit like a suction cup to improve traction. None of this I knew, but upon reading it not only were they incorporated into the story, they added new events to the story which made it seem more real to me the writer. And hopefully more real to the reader. Entire stories can be generated this way. A number of years ago somebody held a contest for transformations of a particular type. I had an idea for using a transformation into a road runner for the 'flightless birds' category. Unfortunately, researching road runners confirmed that they could fly, just not very well and not for long distances. Not only that, but the same article described how a road runner kills a rattle snake by grabbing its tail in its beak, partially swallowing it, and then whipping it back and forth against the ground to kill it. I ended up writing the story in the 'flighted birds' category, using the fact that a road runner can fly as part of the climax, and using the whole bit about killing the rattlesnake as an event within the story. The story won the contest, and it almost certainly wouldn't have done so if I hadn't done some research.

You can even learn useful things from research. For another story, I looked up sites to review basic Calculus to make sure I could explain the basics correctly via a character. When I first took Calculus, we spent the first while on Limits for no reason that I ever understood. Until I researched on the information, and found out that limits are used to derive Differential Calculus. Suddenly it all makes sense!

The internet is out there. You don't need to go to a library, or to quote your sources, you just need to take a look, take some notes, and make use of the vastness of human knowledge.

Your readers will thank you for it.