"Hi, I have an emergency," a distressed boy can be heard telling the operator. "My little brother might be dead."

"OK, why do you think he's dead?" the operator asks.

"Because there's a rope around his neck tied to a bunk bed, and he's all purple and stuff," the crying child says.

There's a shocked silence in the Upper Moreland Middle School auditorium in Hatboro as Metheny, an Upper Moreland Township patrolman, drives home his point.

The taped young voice belongs to Samuel Mordecai, 13, of Paradise, Calif. On May 6, 2005, he found the body of his twin brother, Gabriel, who had strangled himself while playing the choking game.

"These kids are being killed all too often because kids are making a mistake" by playing the game, Metheny, 38, a married father of two, tells the dozen adults present.

He wants the deaths to stop, so he has gone on the road for the nonprofit Games Adolescents Shouldn't Play (GASP). In three years, he estimates, he has spoken 200 times in eight states.

The choking game is a stunt in which adolescents suffocate themselves or each other until they faint, to achieve a brief euphoric state as blood rushes back to oxygen-starved brain cells.

Experts think that children as young as six are playing it. They hear of the game from their peers or learn about it from videos on the Internet.

In the last few years, teens have begun playing it alone using ligatures. When this ends badly, a family member will typically find the child kneeling, still wearing the noose, or hanging from a high object such as a closet door.

It also has become addictive, Metheny and other experts believe. With each repetition, teens run the risk of death or brain injury.

The Centers for Disease Control (CDC) has weighed in. On Feb. 15, it issued the first attempt to assess the national incidence of death among youths because of the choking game.

Using news reports because no agency collects data on these deaths, the CDC estimated that 82 people ages 6 to 19 died between 1995 and 2007.

Among 70 deaths for which detail was available, 95.7 percent occurred while the child was alone, the CDC said.

"Although asphyxial games might have been played by youths for generations, the use of a ligature while playing alone appears to be a new practice that can be fatal," the CDC said in its report.

Of the 82 fatalities, 86.6 percent were male, reflecting boys' tendency to take more risks than girls, the report said. Another finding: In 92.9 percent of cases in which parent detail was offered, parents knew nothing about the choking game until their child died.

But experts disagree on how prevalent it is. Last week, Mark Lepore, professor of counseling psychology at Chatham University in Pittsburgh, read a paper at the American Counseling Association National Conference in Hawaii, giving a darker picture.

His study, covering 1996 to 2006, found 300 confirmed deaths in youths 9 to 18 because of the choking game. The study included choking deaths coupled with auto-eroticism, which the CDC chose to leave out.

Lepore said that even the 300 figure was conservative.

"We believe it was much more," he said. "We were being cautious."

Often, choking-game deaths are hard to find. Many appear on death certificates as suicides, Lepore said. It takes interviews with the victim's siblings or friends, or time spent tracking the victim's Internet movements, to make the connection.

Adolescents playing the game are high achievers and athletic, and have many friends, Lepore and Metheny believe.

"More likely than not, it's the 'good' kids who are doing this," Metheny said. They figure that since the game doesn't involve drugs or alcohol, isn't illegal and hasn't been banned by parents, it must be safe.

But it's not safe, says Stephen Fedder, chief of neurosurgery at Lankenau Hospital. The brain depends on a steady blood flow carrying oxygen and glucose to nourish cells. Without it, cells are damaged in three to five minutes.

If the blood supply is restored immediately, the game player might recover, but with cell loss.

If the player passes out before the ligature can be loosened, "you're in trouble," Fedder said.

Metheny, who began his crusade after youngsters and parents asked about the choking game, worries about whether kids will receive the message in time.

On Dec. 10, 2005, Mitchell Walsh, 11, a fifth grader at Simmons Elementary School in Horsham, was found dead in his bedroom.

Mitchell had tied a cloth belt around his neck, and attached it to a top bunk bed. When he leaned forward to achieve the high, his weight tightened the belt, strangling him, police said.

Horsham students have never heard Metheny speak. Horsham parents heard his warning in January 2006, but by then, it was too late to save Walsh.