The Uncanny Valley

Yet the humans’ skin could not be too realistic.  It was well known that as depictions of humans became more lifelike, audiences would perceive them as more appealing — until the realism reached a certain point, close to human but not quite, when suddenly the depictions would be perceived as repulsive.  The phenomenon, known as the "uncanny valley," had been hypothesized by a Japanese robotics researcher, Masahiro Mori, as early as 1970.  No one knew precisely why it happened, but the sight of nearly human forms seemd to trigger some primeval aversion in onlookers.  Thus, the minute details of human skin, such as pores and hair follicles, were left out of The Incredibles’ characters in favor of a deliberately cartoonlike appearance.

That is from David A. Price’s very interesting The Pixar Touch.  Here is Jason Kottke on The Uncanny Valley.