If you've ever watched a tightrope walker and thought "I could do that!," now is your chance to prove it. At the "Circus! Science Under the Big Top" exhibit at the Maryland Science Center, you can walk on a tightrope nine feet in the air, squish yourself into a contortionist's box and look inside a sword swallower as the blade slides down.

Richard Voelker of Havre de Grace tried the tightrope on a recent Sunday visit to Baltimore. He pulled on a safety harness, stepped onto the inch-wide steel cable and immediately started wobbling.

"Wow, this is fun, but it definitely leaves you a little queasy," the 10-year-old said, laughing.

As with everything else at the show, the science behind the feat gets explained:

Gravity is pulling you down. It is countered by an upward push from the wire. You want the wire pushing up as much of your weight as possible, so you try to keep the center of your weight -- your rump -- balanced over the cable. Friction between your feet and the wire's rough surface keeps you from slipping.

As Richard learned, walking the museum's tightrope gives you a better appreciation of what real funambulists (tightrope walkers) do at higher heights on thinner wires!

For a more down-to-earth experience, the show has a fascinating animal poop display. It's pretty easy to see which deposit was made by an elephant, but telling the difference between tiger and giraffe droppings will challenge you.

As you ponder whether the fleas in the "flea circus" are real or an illusion, you can learn some amazing facts: For instance, fleas can spring 13 inches into the air -- equivalent to you leaping atop a 250-foot building in a single bound.

Speaking of flying through the air, there's a mini-version of the human cannonball act (minus the human): You aim the gun so that the little ball lands in the safety net. For circuses that had human cannonballs, getting the right arc and speed could be a life-and-death matter for daredevil performers.

As for sword swallowing, if you've suspected it was done with a collapsible blade, think again. As you push on a sword's shaft, an X-ray-type video shows the actual path a 22-inch-long blade takes after it is lowered into a sword swallower's throat.

You might have to do what the swallower did to accomplish this feat: Suppress your gag reflex!

-- Fern Shen

A walk on the tightrope gives kids an exciting lesson in friction, centering their weight, and -- if all else fails -- gravity.What's it like to fly at a circus? Andie Himmelrich, 9, learns about human cannonball acts, above, and trapeze-like flips, right.