[Tancred]

Ok!

The first thing I suggest you is tou use a progam named Blender. It is a FREE 3D program that gives professionnal results. In fact, some pro are using it and you can easily find tutorials for it.

Now, if you use digital FX, here are some things you need to know :

1) If you use a tripod and don't move your camera, you won't have to track your shot wich means it will be a lot easier to integrate the effect.

2) NO COMPRESSION. Alway use the best quality your camera can makes. If you don't your effect will look fake.

3) Add the grain. To make your effect more realistic, you must add your camera grain. You can try to match it with the tools of After Effect or simply film a gray pannel and past it on your effect (but not on your shot) with the overlay fusion mode.

Now, what I see two technics you could use to create the hairs.

1) The simpliest (but not as realistic as the second)
You'll need to learn how to use the hair tool of Blender. Basically, you create a 3D geometry that looks like the surface you what to make hairy.

Then, you create a very light coat of fur on it. For the render, you hide your geometry, but not your hair.

You can also can create a shaddow pass by making your geometry visible and hiding the primary ray of your hairs.

You redo this step many times and you'll get some different hair textures that you can reveal progressively one after the other and, by justabosition that will give the impression the coat of fur is getting more and more thick.


2) The hardest one.
This is probably the technic that have been used for the "Define Beauty" video.

For this, you'll have to learn how to use the particles of Blender.

You still have to have a geometry that looks like your model, but, this time, you'll just have your hair pass and your shaddow pass to make once.

The particles can take many forms. One of them is a strend wich are kind of lines. By emetting particles from your geometry with strends and a good render material, you'll be able to create hairs and you will be able to make them grow.

I'm not a Blender user, but those technics works in any 3D programs. I also would like to say that I am a professionnal FX artist. It is what I do to pay my bills and everything so I guest I know what I'm talking about! Lol! I would also like to suggest you to try Nuke instead of Aftereffect. It is a lot more powerfull. ;-)