Dan said that if he does decide to amputate his leg, he would consider it a "rational" act. "Having my leg off would cause a handicap and suffering," he said. "But BIID also causes handicap and suffering, and it's just a matter of which is worse."
Most doctors consider the act of removing a perfectly healthy leg or arm to be unethical. Unfortunately, that doesn't stop the obsession. In fact, Dan's obsession got so bad last year that he searched and located a surgeon in the Philippines who would perform an amputation for a price -- one leg for $10,000.
In the end, Dan said the steep price and questions about the surgeon's competence kept him from following through.
Lilly, however, was determined to finish the job. She mutilated her left leg last year by freezing it with dry ice, hoping doctors would be forced to amputate it.
"I have no more ankle. My foot is swollen all the time," she said.
So far, doctors have not complied with her wishes.
Lilly (who also asked that her real name not be used), like Karl and Dan, said her obsession began in childhood. "I used to play that I was an amputee," she said. "In that little world I was normal. I felt complete. ... I felt good."
Lilly also knew exactly where she would want each of her legs to end -- with the right leg two centimeters longer than the left.
For years, Lilly kept her strange wish locked deep inside her, even after she married and started a family in a little French town on the Mediterranean Sea.
But her husband, George, said there were signs that things were not quite right. "She used to do things that didn't make sense," he said. "She used to bandage up her legs, especially at night when she was alone."
Lilly said when she told her personal physician in France about her obsession, he said that if she went through with it, he would have her committed to a mental institution. Eventually, Lilly confessed to George.
George was understandably shocked, but he ended up standing by his wife. And Lilly began looking for a surgeon who would help.
In the late 1990s, a British surgeon named Robert Smith amputated the legs of two physically healthy patients at a hospital in Scotland, sparking a furor in the British press.
Smith said he performed the surgery to end his patients' obsessions and suffering. "They may take the law into their own hands," Smith said. "They may lie under a railroad line, on a railroad line and get run over by a train. They use shotguns and shoot their limbs off. They really are a desperate bunch."
And Lilly was indeed desperate. When she learned about Smith, she and George traveled to the hospital in Scotland where he worked. She froze her legs in dry ice near the hospital.
But Lilly could not stand the intense pain long enough. By the time she entered the hospital, her legs were badly damaged but there would be no amputation.
The ordeal has left her crippled but unbowed in her quest for an amputation, and Lilly said she has no explanation as to why.
Her husband, George, continues to help her. "It is difficult because it's not a normal thing to do," he said. "It is her body and she's gonna do it. I'd rather be there and make sure that no one gets more hurt, and that she doesn't lose her life doing it."
Today Lilly, Dan and Karl all chat on the Internet occasionally, though Karl's story has taken a sobering turn.
Karl said his obsession with losing a limb did not end with his double amputation. But he said he finally lost his desire to also remove his left hand after an intense regime of therapy and anti-depressants.
For a man remarkably at home in his wheelchair, there is a hint of regret. There are places the wheelchair can't take him, like to the beach to feel the sand under his feet.
"It's all those little things, like that," Karl said. "What the hell was I thinking?"