Bob Burwell, ruddy Australian and crack boomerang thrower, examined the artfully curved stick in his lap. "Gurkha Kris Fighting Knife," read the label. It was a boomerang, of course.

"You know," he said in the cadence of Brisbane, where he works as a communications tradesman, "I served with Gurkhas in Borneo during the Indonesian confrontation, about 1965. They were Gurkhas from Nepal."

He sipped his soda-water, scratched his jetblack pate. "Some people once were blocking their passage across a road, and a Gurkha went to the nearest person who was being obstructive, slashed his head off with one of these cookery knives, and stuck it on the hood of a truck. That did the trick."

He grinned. "In actual fact, the Gurkhas have an annual tradition of beheading things. They start with small things, like chickens, and work all the way up to a large calf. And when they miss, they put nicks in their wrists for shame."

It the Washington digs of Benjamin Ruhe, boomerang maven nonpareil, Burwell's American listeners giggled; an Australian compatriot shrugged. Chats with fans of boomerangs, like the flying marvel itself, have a way of taking surprising turns.

You can witness such for yourself this Saturday, when the Smithsonian's Ninth Annual Open Boomerang Festival -- a.k.a. the "Now-You-See-It, Now-You-Don't, Now-You-See-It-Again" tournament -- brings hundreds of folk from hither and yon to West Potomac Park. There'll be basic throwing and catching for neophytes; juggling, catching blindfold and other stunts for experts.

"We'll do it even if it rains," said the irrepressible Ruhe, the festival's founder, who's called The Scholar in boomerang circles, often in tones of reverence. "The only thing that would stop us would be very high winds."

The other night he was huddled in his den with Burwell, who'd arrived via boomerang bouts in Portland, Oregon; Dr. Peter Johnson, an Australian economist just off the plane; and Floridian Rusty Harding, an erstwhile engineer who makes boomerangs for a living. Though the talk sometimes strayed to the habits of Gurkhas, it always returned to the aboriginal point, with the Yanks drinking beer and the Aussies unaccountably sipping soda-water.

"When boomerang freaks get together they talk about boomerangs," said Ruhe, who was seduced by the objects at Botany Bay, on a long-ago lark Down Under, and returned last fall to lead Americans in combat. ("America 3, Australia 0 -- that was the score at the end of the world's first boomerang Test series. And we should hang our heads in shame," the Sydney Telegraph said.)

"We didn't let them beat us at all," said Burwell, who holds his country's boomerang distance record with a toss of 111 yards out and back. "The Americans were just better."

Last Saturday, in his dash for B-Day, Ruhe delivered a boomerang lecture, screened boomerang movies -- one showed a gentleman in the buff, rump to camera, doing a boomerang dance that resembled the Charleston -- told boomerang jokes, passed out boomerangs and presided at boomerang lessons in a squishy-wet field.

"It's easy to say what a boomerang is not," declaimed Ruhe, the recently riffed press officer of the National Archives, who sells boomerangs along with his book, Many Happy Returns: The Art and Sport of Boomeranging.

"It is not," he told his audience at the Museum of American History, "a bunch of grapes that you throw into the wind, which then forces it back to you. It is much harder to say what a boomerang is."

Fraught with magic -- "This is a very complicated subject," he warned -- the boomerang flies in dizzying shapes and sizes. There is, for instance, the throw stick, a curved length of wood tht soars but doesn't return. It was this device, Ruhe said, with which Australian aborigines killed beasts in the Outback; nowadays they favor .22 rifles.

The famous returning boomerang was rarely if ever a hunting tool: Then as now it was for fun and games. Invented thousands of years ago, it is basically an elongated V, rounded almost to a C, with one side flat and the other curved. Hurled slightly cross wind with a snap of the wrist, it curves out perhaps 30 yards, climbs, dives and shoots back -- all the while whirling like a roter-blade.

Much of the rest is mystery.

"A fellow I know, a Dutch physicist named Felix Hess, spent seven years doing his doctoral thesis on boomerang flight," Ruhe said, plucking odd-shaped missiles from a kangaroo skin and handing them out: boomerangs like the letters "A" "E" and "Omega," boomerangs like pretzels and one like Napoleon's hat. "When Hess finished, he said he was almost sorry he'd started. The thing was just too complex."

Hess used a computer to plot theoretical journeys; another investigator, Belgian Yves Simonson, is currently doing the same. "I'm using a more powerful machine, so perhaps my models will be, how you say, a little sexier," said the 28-year-old computer whiz. "It's a lot of fun."

His lecture over, Ruhe having tossed and retrieved a cardboard model indoors, he and other stalwarts -- a Department of Energy engineer, a Department of Defense computer type, and a professional futurist among them -- braved drizzle and mud for some throws and instruction.

Peter Cashin, a communications consultant, brought a few of his own making. "My father was a veterinarian in Tunkhannock, Pennsylvania," he said. "He used to buy boomerangs mail-order and take them out with him on his rounds. He'd get finished with a call, the farmers would be standing around shooting the breeze, and my father would grab a boomerang and start throwing it around. They'd all be just amazed. One time, he broke some windows of a station wagon; another time, he hit a guy in the knees."

Arnold Weintraub, the energy engineer, hurled a model he picked up a couple of years ago at the Tralee Sheep Station in New Zealand. "I like to flip it around a little during lunch hour," he said. "It's a gentle exercise, and the aerodynamics are fascinating."

Bob Coakley, the Defense man, turned out in a T-shirt that read "Boomerangs are as American as Kangaroos," taught but didn't throw. "I've got boomerang shoulder," he complained.

Jerry Glenn, a pipe-smoking futurist, stowed one of Cashin's models between his teeth and launched a second one, letting it knock the first out of his mouth on the return trip. "I don't remember who my dentist is," he said. "So far, my teeth are okay." MANY HAPPY RETURNS

The Smithsonian's Ninth Annual Open Boomerang Festival, Ben Ruhe presiding, starts at 1:30 Saturday at the Polo Field, south of the Lincoln Memorial in West Potomac Park. Novices and experts are invited to compete, and spectators to watch, all for free. Starting at 2:30, there'll be demonstrations of spear-throwing, didgereedoo playing and aboriginal firemaking.