CBP arrested a 21-year-old woman at the Atlanta airport who smuggled three pounds of cocaine in the soles of seven pairs of shoes.

According to a CBP news release, the street value of the substance was approximately $40,000. The unidentified woman was traveling back to the U.S. from Jamaica on Sunday. “Shoes are made for walking and not smuggling narcotics,” CBP said.

Agents flagged her for further inspection after her arrival, though it wasn’t revealed why. Officers then discovered a “white powdery substance” in the bottom of the shoes, which ranged from sandals to sneakers and wedges. The substance later tested positive for cocaine. CBP shared images of the shoes and of an agent taking them apart on the table. A pack of cocaine can be seen stuffed into the shoe’s sole.

“Smugglers go through great lengths to conceal drugs from our officers,” said Paula Rivera, CBP Port Director for the Area Port of Atlanta. “Narcotics interdiction remains a priority CBP enforcement mission, one that we take very seriously.” On an average day, CBP seizes 3,677 pounds of drugs from people traveling in the U.S.

In fact, smuggling drugs in the soles of shoes has almost been a tried-and-true method. Back in December, a CBP drug-sniffing dog found over a pound of fentanyl that was duct-taped in shoes in Yuma, Arizona.

CBP handed the woman over to the local police department for state prosecution.