The waterfall that flows uphill.
A card trick that works no matter how many times you do it.
The Chinese acrobat whose backbends turn her into a human doughnut.
They attract and titillate and trouble us all at once because they aren't normal, said Rand Ziegler, chair of the psychology department at Baker University in Baldwin.
We are used to seeing water flow downhill.
We know a computer can't read our minds.
And people are supposed to bend forwards, not backwards.
With each passing day we become more convinced that there is order in the world, that people far away aren't any smaller than the people standing next to us, that you can't guess a card from a 52 card deck consistently.
"Nature kind of preprograms us to develop these expectations. Our experience kind of stamps it in," Ziegler said. "With illusions, we have all of a sudden things that defy our expectations."
That's what drove Walter Wick to put together his latest book, "Walter Wick's Optical Tricks."
"I've been intrigued with them (optical illusions) since I was very young, probably about 7 or 8," Wick said from his Winsted, Conn., studio.
Known for his child-loved series of "I Spy" books, the more recent book is filled with photographs that constitute optical illusions.
"On a deeper level, optical illusions are really demonstrative of how much the mind is involved in what it is you are seeing," Wick said. "When you realize the truth of what you are looking at, it's amazing to find out it can look so false."
The jaw-dropping or furrowed brow of surprise are the same for Wick's confusing photos as they are for the magician's audience.
"A good optical illusion has the quality of a good magic trick," Wick said. "It's really up to the artist to create magic in terms of making something seem more incredible than it really is."
That is certainly the case for an Internet card trick that appears to read minds by selecting a carefully chosen card time and time again.
The site at http://www3.mcps.k12.md.us/users/rsfay/magic/index.html is called the Cave of Magic.
It invites visitors to chose one of six cards being displayed. Two mouse clicks later, only five cards remain. The chosen card is gone.
It seems to be magic. But is it? An explanation can be found on page 3D.
Ziegler said that like an optical illusion or the Chinese acrobats who visited Baker University recently, the computer card trick is amazing because it is unexpected.
"We expect the stop sign to be red," he said. "We'd freak out if we saw a green stop sign."
-- Kendrick Blackwood's phone message number is 832-7221. His e-mail address is email@example.com.