I suppose you expect us to entirely ignore Jack Handy's answer, huh?

Boxing Kangaroos continue to be a menace, I've heard.

But seriously. Which is scarier: shark? Crocodile? Mountain-lion-with-taste-for-jogger? Bear-warped-by-too-much-casual-human-incursion-into-habitat?

I forgot to add ostriches. Ostriches are really damn scary.

How about little worms and stuff that crawl into and make home in your skin?

Are bacteria animals? Or they a third kingdom? I forget. I think they're animals (or plants, if they have chlorophyll). Those flesh eating bacteria are pretty scary.

Those are all pretty scary, but I think the wombat is going for the "oh my gawd it's gonna freakin' tear me apart" feeling. I think the more dinosaur like the critters get, the more visceral my fear. So, indeed, Ostriches are freaking scary. But Alligators/Crocodiles are much much scarier. Round these parts, anyway, you really have to go out of your way to get in the teeth of a shark. Ostriches generally confined to burgers. But Alligators/Crocodiles can get you by land, sea, or toilet.

Funny that we're all much more likely to be done in by the invisible critters mentioned above. Or bears.

I sort of agree about crocodiles actually (my nightmare animal growing up was the big bad wolf, but that's more a monster out of folklore and sadistic children's literature). David Quammen's excellent book Monster of God discusses the human experience with big predators around the world, and the stuff on crocodiles was far scarier to me than that on bears or man-eating tigers. He writes about one woman's experience in Australia (it seems that conversations on the WFile always return to our spiritual home down under) in which she was pursued while in her canoe by a large croc. She foolishly grabbed onto an overhanging tree branch, thinking to pull herself up out of range completely, but the croc grabbed her like a dangling meat-treat and pulled her under.

Then the crocodile did something that is apparently referred to as "the death roll." And that's when I promoted the croc to No. 1 scariest animal in my imagination. Note: the woman lived and wrote about the experience in an essay titled, shiver, "Being Prey."

If you've ever been attacked by a troop of monkeys, you'd know fear. It doesn't matter that they're not carnivorous - it's the SWARMING of the beasts that you can't escape, and their cunning in cutting off your escape routes, which is truly terrifying. You can't fend them off with rocks, as you can with a packs of mangy dogs - they'll just throw 'em right back. If any pack of carnivorous, toothy animals came my way, fuggedaboudit. That would be scarier than MIDDLE SCHOOL.

Also I would nominate eels and scorpions.

i agree about the monkeys. once I foolishly bought some bananas from an old woman and walked right into the monkey forest in Ubud, Bali. if'n i hadn't been wearing long pants that day, i'd have lost the flesh on my legs. and these were tourist-friendly monkeys. they _do_ enjoy bananas.

I also nominate the big cats--watching a small cat disembowel a toy is enough to give one pause; i'd rather not have a tiger bite me on the head and kick start my stomach.

Centipedes and millipedes -- that icky swarming action and the un-hairy hairiness. Also they tend to run right at you rather than away from you. And they bite. Well, the centipedes do.

Never trust a bird.