For over twenty years, scientists have used modern technology, in the form of CT scans and X-rays, to virtually unwrap mummified remains. These powerful tools, which allow researchers to peer inside mummies, provide information as to cause of death, burial treatment, and individual traits of the deceased. But now, this technology is being used to explore a new breed of Egyptian mummies: animals that were preserved to accompany the dead. And perhaps the greatest surprise is what's missing from these mummified treasures.

Researchers at the Manchester Museum in England set out to explore the practice of animal mummification, which began around 3,000 BC and peaked from 650 BC to AD 200. Some 70 million animals may have been mummified by the Egyptians and the Manchester team has scanned some 800 of them, from cats to birds to crocodiles.

"We know the Egyptians worshipped gods in animal forms, and an animal mummy allowed you some connection with the world of the gods," Dr. Campbell Price says. Price is curator of Egypt and Sudan at Manchester Museum, which will have an exhibition on animal mummies in October.

"Animal mummies were votive gifts. Today you'd have a candle in a cathedral; in Egyptian times you would have an animal mummy. You would go to a special site, buy an animal mummy, using a system of barter. You'd then give it to a priest, who would collect a group of animal mummies and bury them."

But what astounded the researchers was not what they found within the mummies, but what they didn't find. About a third of those scanned contained no animals whatsoever.

Dr. Lidija McKnight, an Egyptologist from the University of Manchester, says that "There have been some surprises. We always knew that not all animal mummies contained what we expected them to contain, but we found around a third don't contain any animal material at all - so no skeletal remains."

What the researchers found was a strange mix of organic debris.

"Basically, organic material such as mud, sticks and reeds, that would have been lying around the embalmers workshops, and also things like eggshells and feathers, which were associated with the animals, but aren't the animals themselves," McKnight says.

Researchers speculate that the industry simply couldn't keep up with demand, despite the fact that animals were mass-bred to accommodate the practice. And although the false mummies were not what they appeared, the folks at Manchester Museum abstain from labeling them as hoaxes.

"We think they were mummifying pieces of animals that were lying around, or materials associated with the animals during their lifetime - so nest material or eggshells. They were special because they had been in close proximity with the animals - even though they weren't the animals themselves."

"So we don't think it's forgery or fakery. It's just that they were using everything they could find. And often the most beautifully wrapped mummies don't contain the animal remains themselves."