I've found the most disturbing animation since the Crack Master cartoon on Sesame Street. It's from Fantastic Planet, a French/Czech film made in 1973, directed by Rene Laloux. Leonard Maltin called it "static," "aloof," and "worthwhile." Leonard's funny that way.
There are a number of clips of this on YouTube (apparently, it's in the public domain), but I'll introduce you the way I was introduced - with this particular trailer.