Scientists studying animal mummies from Ancient Egypt have found that lots of them don't actually contain any animal remains.
Researchers at the University of Manchester scanned more than 800 animal mummies to see what was really hidden beneath the bandages.
About a third contained complete animal remains, a third had bits of animal remains and the rest were empty, filled with things like mud, eggshells and nest material instead.
But the researchers don't think it was done as a scam. Those buying them may have known they weren't complete mummies.
Instead they think there was such a high demand for mummified animals in Ancient Egypt, that the makers resorted to using other things instead to keep up.
Scientist Dr Lidija McKnight says: "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.
Why did Ancient Egyptians mummify animals?
Ancient Egyptians worshipped gods in animal forms and animal mummies were used as a type of religious gift.
Dr McKnight says: "You would go to a special site, buy an animal mummy.
You'd then give it to a priest, who would collect a group of animal mummies and bury them."