A shipment of 18 frozen human heads was discovered and seized by customs officials during an X-ray screening of cargo that arrived at Chicago's O'Hare International Airport on Tuesday.

While the realization of the craniums was indeed eerie, they were used for medical research in Italy and were simply being sent back to Illinois to be cremated. The holdup was because of a paperwork discrepancy, according to Yahoo!

Once federal authorities confirmed the paperwork, the specimens will be given to the cremation service, said Mary Paleologos, a spokesperson for the Cook County Medical Examiner's Office.

Originally the heads were sent from Illinois to a Rome medical research facility and returned to Chicago as part of a disposal agreement. A cremation service arrived at the Medical Examiner's Office with paperwork for the heads.

Such means of shipment is considered common, as the body specimens are known to be transported across the globe by aircrafts and delivery trucks, according to the news report.

"Just last week, we transported eight heads, un-embalmed, to Rush University Medical Center for an ophthalmology program," said Paul Dudek, vice president of the Anatomical Gift Association of Illinois, which gives cadavers and body parts to medical schools in the state for the training of students.

The respective association sends out roughly 450 whole cadavers to medical institutions each year and individual body parts as well, which includes about a dozen shipments of heads annually. The craniums are used for dentistry, ophthalmology and neurology, amongst other training related programs.

Most of the cadavers are received through a voluntary donation by individuals who give permission for their bodies to be used for the benefit of science upon their death. A smaller portion of the cadavers are said to be from families who can't afford a burial and agreed to allow the state to release them for research.