Clamp fits like a boot on an illegally parked car.
Rape-aXe is a flexible polyurethane condom-like tube that fits into the woman's body. Rows of jagged plastic hooks line the inside of the tube - bent backward like teeth in a shark's mouth - and lodge in a perpetrator's penis upon entry. The perpetrator can withdraw from the woman, but the Rape-aXe remains clamped on. Trying to pull it off will cause discomfort.
Though the device causes great distress, it does not draw blood, Ehlers says, which is crucial in areas where HIV/AIDS rates are high. A man must seek medical attention to have the Rape-aXe removed. Until then, he cannot urinate, essentially tagging him until he gets to a hospital, she explains. Ehlers says she consulted an engineer, gynecologist and psychologist on the design.
Grace Faraja, 29, has lived through the constant fear of being raped. She lived most of her life in Kinshasa, the capital of the Democratic Republic of the Congo, before being granted refugee status and moving to New Hampshire in 2008. She says that if she were back in Congo, she would wear the Rape-aXe.
"What people need is this condom," Faraja says. Especially when women are most vulnerable, at night and when traveling from one town to the next, she says. "When men hear about this," Faraja says, "they will be scared. They won't know who has protected herself and who not."
But some critics are doubtful that the Rape-aXe will benefit women in conflict zones, where rape is used systematically as a weapon of war.
"Maybe that makes sense in the First World," says filmmaker Lisa F. Jackson, who interviewed rape victims and rapists in the Democratic Republic of the Congo and produced "The Greatest Silence." Jackson estimates that more than 200,000 women and girls have been raped since the civil war began in 1998.
"But if a guy is raping you, and there's five other guys waiting to take their turn … do you think he's going to take that well? They're going to mutilate that woman. It's just a provocation."
The Rape-aXe is a latex sheath containing sharp barbs that latch onto the penis when a man tries to rape a woman. The device can only be removed surgically.
But Ehlers, who created the device, says that the benefits outweigh the risks. What is already a violent and often deadly incident cannot be made more violent, she says. "I'm trying to get these women a moment, that's all."
Women already have been arming themselves with homemade defenses - a razor blade hidden in a vaginal sponge or razor blades glued to the inside of a plastic cap that is worn in the vagina. Some South African women have taken to wearing bicycle shorts so short and so tight that cannot be yanked off, Ehlers says.
In South Africa, which has been dubbed the rape capital of the world, women are begging for access to the device, Ehlers says. A 2006 Interpol study found that a woman is raped every 17 seconds in South Africa. A separate study found that of more than 20,000 reports of rape across South Africa, only 8 percent led to a conviction, according to a 2009 Amnesty International report.
With the Rape-aXe, "at least the police have this man," Ehlers says. "But now he rapes, now at least the possibility of getting him sooner is there before he kills more women."
But the device remains unavailable to the public. In fact, its "teeth" have yet to bite into a real penis, though it has been tested without the barbs attached. One man from the U.K. has offered to be the first, though his motives are unclear.
Ehlers will not release the Rape-aXe until she is able to first distribute the devices to South African women. She plans to distribute 30,000 at no cost, and hopefully before the World Cup games in June, she says. They will cost less than $2 each thereafter.
"Women try to fight, to save themselves, but you can't fight men," Faraja says. "You don't know when they're going to rape you, you can't walk with a weapon. It comes abruptly ... It's done in darkness."
This report comes from journalists in our Student Correspondent Corps, a GlobalPost project training the next generation of foreign correspondents while they study abroad. Student Louise Ward (Boston College) contributed to this report.