Animals do not turn into zombies — only humans do. At least, that seems to be the rule so far in AMC's sci-fi zombie thriller, "The Walking Dead" (which airs Sundays at 9 p.m. EST/8 p.m. CST).

Some species of viruses, fungi, protozoans, wasps, and tapeworms take over the brains and actions of the animals and insects ... which turn their hosts into zombies. This is usually controlled ...

Therefore, Mr. Smith says, "Whatever the cause, the symptoms of zombieization are considered to be peculiar to humans at the moment, otherwise they should be watching zombies of animals somewhere ...

It may sound like something straight out of a horror movie, but many animals can come under the zombie-like control of parasites. So what about humans? Scientific American editor Katherine Harmon ...