On zombies.

Zombies have been described in many ways, but from a logical point of view, a successful zombie is pretty easy to imagine: a fast, live human infected by a virus with an incubation period of two to four weeks.  Fast because an effective vector virus would use its victims' abilities to transmit it to other potential victims, like one of rabies' strains does.  People can run, so why not these zombies?  Corpses don't move all that much either, so obviously you need a live victim.  There are other possible culprits for zombiism (that's now a word), but they all have problems compared to the virus option: parasites are more difficult to transmit, bacteria aren't "smart" enough to rewire your brain, and chemicals just don't do that sort of thing.  Radiation?  No.  Viruses are also pretty good at multiplying, so the onset will be reasonably rapid, but it will take weeks; viruses can explode in population once they've gotten started in the body but they still take time to get up to force, and taking over a brain to any degree isn't a simple job.

All that is kind of obvious.

Antlion.