Since airport security began using some controversial methods for keeping travelers safe, there have been numerous stories in the news about the things airport officials find hidden in luggage or in the possession of people coming through. But this is the first we’ve heard of human body parts trying to find their way through customs.

When airport employees scanned in a shipment of cargo at O’Hare International in Chicago, they got a huge surprise: 18 frozen human heads which were being returned from a medical research lab in Italy to a crematorium in Illinois. Apparently the paperwork accompanying the heads caused some confusion for the employees at customs, creating a holdup in the system. What’s more surprising is that human body parts are shipped all over the country all the time for medical research, often without the public being any the wiser.

“Just last week, we transported eight heads, unembalmed, to Rush University Medical Center for an ophthalmology program,” said Paul Dudek, director of the Anatomical Gift Association of Illinois.