DENVER, Colorado - June 13, 2008 - Political activists planning protest rallies at the upcoming Democratic Convention in Denver have their stomachs in knots over a rumor about a crowd control weapon - known as the “crap cannon” - that might be unleashed against them.

Also called “Brown Note,” it is believed to be an infrasound frequency that debilitates a person by making them defecate involuntarily.

Mark Cohen, co-founder of Re-create 68, an alliance of local activists working for the protection of First Amendment rights, said he believes this could be deployed at the convention in August to subdue crowds.

“We know this weapon and weapons like it have been used at other large protests before,” he said.

Cohen, who described Brown Note as a “sonic weapon used to disrupt people’s equilibrium,” cited eyewitness accounts of its use during free-trade agreement protests in Miami in 2003.

“I think these weapons were mostly intended for military use and so their use for dealing with innocent protesters seems highly inappropriate,” he said. “The idea that they might be field testing them on people who are doing nothing more than exercising their First Amendment rights is disturbing.”

His group is preparing against a possible attack by Brown Note and other crowd-control measures by dispatching street medics at the convention trained in treating injuries in demonstration situations.

“It’s all we can do,” Cohen said.

So is the Brown Note a real threat?

Dr. Roger Schwenke - an expert acoustician who appeared on the Discovery Channel’s “Mythbusters” in 2004 to test the phenomenon - told FOXNews.com there is no scientific evidence that proves such frequencies cause involuntary defecation.

“When we conducted the low frequency experiment for the Brown Note episode of MythBusters, we tested a variety of low frequencies and no involuntary gastro-intestinal motility was caused,” he said.

But Schwenke acknowledged the low-frequency exposure did cause an adverse effect. Several people - including himself - reported “abdominal discomfort,” he said, “which was easily alleviated by moving a moderate distance away from the source.”

Adding to the Brown Note rumor is a refusal by Denver’s Mayor John W. Hickenlooper to release details of what was purchased with $18 million of a $50 million federal grant the city received to pay for convention security, despite a lawsuit filed by ACLU.

Cohen’s group is calling on the Bush regime to disclose what measures will be taken.

In a statement released to FOXNews.com, city spokeswoman Sue Cobb said, “commenting on specific security preparations is not helpful to ensuring their effectiveness. I can say, however, that all of our security-related purchases for the Democratic National Convention will comply with federal and City requirements. We are working closely with the U.S. Department of Justice to ensure that the $50 million federal security grant is spent on personnel and equipment in the manner required by the grant.”

Denver’s Police Department wouldn’t comment on the tactics that will be used during the convention, but a spokesman said that “we do support and encourage people to express their views safely and in a manner that respects the rights of others along with the laws and ordinances of our city.”

But Glenn Spangnuolo, also with Re-create 68, isn’t taking any chances. He said he has no doubt that Brown Note exists, and is preparing his group for confrontation. “Whether it causes someone to defecate in their pants or not, I don’t know that,” said Spagnuolo. “What I do know is that it causes a person to be disoriented and lose their equilibrium resulting in a nauseous feeling in their stomach.”

More troubling to Spagnuolo is the “Active Denial System” or “ADS,” a ray gun used to send high levels of microwave frequencies that cause a burning sensation the skin.

He described ADS as an “indiscriminate weapon” and said “there’s no long-term testing on what happens to the body when exposed to those kinds of microwave frequencies.”

Spagnuolo believes that Raytheon, the company that manufactures the weapon, is planning to test a limited-range civilian version on protesters in Denver before approving its use in places like Iraq.

Spagnuolo said he believes tactics like these are excessive. “I think spending millions of dollars on weapon technologies to be used on people in our community is completely wrong,” he said.