Researchers at the University of Hong Kong say it appears the virus may have come from a civit cat - a racoon-like animal native to Asia and North Africa which is sometimes eaten in China.
The university's medical school is planning a news conference to explain its theory, which is compatible with earlier theories by other scientists who said the disease must have originated in another species and then crossed over to humans.
In Britain, an even bigger crossover is being talked about - by scientists who believe SARS came from outer space.
Writing in the prestigious medical journal The Lancet, the researchers argue that "a small amount of the culprit virus introduced into the stratosphere could make a first tentative fall out east of the great mountain range of the Himalayas, where the stratosphere is thinnest, followed by sporadic deposits in neighbouring areas."
For those who know the lead author, Chandra Wickramasinghe, the theory isn't as surprising as one might think. For decades, he has been one of the leading proponents of "panspermia" - the idea that life on earth originated from, and continues to be seeded by, bacteria and viruses brought into the Earth's atmosphere by means of comets.
The suggestion that SARS is a visitor from beyond raises eyebrows in more than a few halls of academia.
"You don't have to go to Mars to get a coronavirus," says Dr. Donald Low, one of Canada's leading microbiologists and the head of microbiology at Mount Sinai Hospital in Toronto. "A viral particle - where it's RNA or DNA - being able to survive entry into our atmosphere and then fall to Earth in an infectious form just is a little bit beyond me."
As the scientific community debated those developments, the World Health Organization Friday canceled its SARS-sparked warning against travel to Hong Kong and the Chinese province of Guangdong, where the virus is believed to have originated.
The U.N. agency says it lifted the travel warning because the outbreaks of the pneumonia-like disease are under control in both places, and the number of new cases in those regions is declining, along with the number of people still in the hospital.
Also Friday, a U.S. doctor who was helping Taiwan battle SARS left Taipei on a charter plane for the U.S., after developing a fever and other symptoms associated with the virus.
The doctor, an infection control expert Taiwan identifies as Chesley Richards Jr., wore a protective cap, gown, face mask and eye shield as he boarded the air ambulance.
Taiwanese officials say he has not tested positive for the new type of corona virus believed to cause SARS, but the test is not always accurate.
Three other Centers for Disease Control employees who have treated Richards and may have been exposed to whatever he has were also sent back to the U.S. with him.
The group is expected to arrive in Atlanta by Sunday.