"One was: their skin color looks fecal. The other was: their bone structure doesn’t look human. And they’re just off-reference enough to be much more creepy than if they looked less like people, like bad CGI or shambling undead in a B movie. When I paid close enough attention, these were the three basic data under the revulsion; my hindbrain thought it was surrounded by alien shit zombies."
"One was: their skin color looks fecal. The other was: their bone structure doesn’t look human. And they’re just off-reference enough to be much more creepy than if they looked less like people, like bad CGI or shambling undead in a B movie. When I paid close enough attention, these were the three basic data under the revulsion; my hindbrain thought it was surrounded by alien shit zombies."
and http://esr.ibiblio.org/?p=4256