An international treaty prohibits the buying and selling of products made from any of the big cat species, save one: the African lion. If the animals have been bred in captivity in South Africa, then their skeletons, including claws and teeth, may be traded around the world.

Lion parts legally exported from South Africa usually wind up in Asia, where they are often marketed as tiger parts. This lucrative business is on the rise, and according to recent research a ban enacted by the United States may have helped to ignite it.

In 2016, the Fish and Wildlife Service banned imports of captive-bred lion trophies. For many lion breeders in South Africa, skeleton exports were an obvious way to make up for lost business.

“Sometimes, you think you’re doing the right thing, but the outcome of your policy decision is that something worse materializes,” said Michael ‘t Sas-Rolfes, a doctoral candidate at University of Oxford in England who has studied the trade in lion bones.