In monitoring packages sent to the U.S. from abroad, Customs and Border Protection officers regularly seize such things as illegal prescription drugs, narcotics, live animals and even an occasional person who’s trying to avoid spending money on airfare. But on Wednesday, they took possession of something they’d never seized before: a human brain.

The brain, which was in a mason jar, was discovered during an inspection of a Canadian mail truck that had just crossed the border, according to the CBP. It had been sent from a location in Canada and was en route to Kenosha, Wisconsin, officers say.

Although the jar was labeled “Antique Teaching Specimen,” CBP officers say importing brains is a no-no — regardless of whether it’s being used to educate future medical professionals. “Individuals looking to import shipments such as this need to remember that the Centers for Disease Control and Prevention has a strict Import Permit Program that must be adhered to,” says Area Port Director Michael Fox. “This is just another great example of just one of the many things CBP officers do to protect our nation on a daily basis.”