What kind of build type is this?

[Gatto Spingflower]

i have seen in SL a few avatars representing several cartoon characters, what caught my atention was the outlines they look like black drawing lines, but they are showed only from certain view angles! i dont have pictures to showm but for those who are older may have saw same thing on the "south park" avatars out there in SL. if someone can tell me what kind type of build is that and or how to do it!!?? thank you!

[Void Singer]

the effect is called cel shading, and can be achieved by placing a lager version of the same object in the same space, but slighly bigger, making it's exterior transparent, and texturing/coloring the interior.

[Gatto Spingflower]

Thank you! i will try and see how looks.