"Some people don't appreciate that [computer animation] is an art form. They think that there's a button that's like 'Make Movie' and that it just gets done. The computers want to do everything exactly and cleanly and evenly, not organically. If you wanna do that they can do it no problem. But if you want them to present anything that approximates the natural world, they will fight you any step of the way. Less so now. But all of those flaws that you see on 'Ratatouille' on the kitchen floor, each one of those tiles is on a slightly different level. Somebody had to do that because the computer wants to do that exact; everything perfect in its place. If you want imperfections you have to tell the computer, I don't want them to match, I want them to be asymmetrical. And that was done because, through research, when you have actual tiles that have been around in a kitchen that long, they're different, so light hits them differently."
Read more insightful stuff from director Brad Bird here.