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ROCK HILL, S.C. — A South Carolina woman who thought she was unboxing the yoga mat she had ordered from Walmart found something much more nefarious — $400,000 in oxycodone pills, according to WSOC.

The woman, who did not want to be identified, quickly called police and reported the illegal shipment.

Police estimate the bag inside a cardboard box contained roughly 20,000 pills — so many, the woman said, they were spilling from the package.

Police said it appears the dealers tried to send the package from Newport Beach, California, to the woman’s old address in Rock Hill, South Carolina. Her old condominium is currently vacant.

Marvin Brown, commander of the York County Multijurisdictional Drug Enforcement Unit, told the Rock Hill Herald that criminals will often ship drugs to empty homes or addresses where they know the occupants will be away during the delivery.

The dealers then track the package and wait in front of the house for the delivery truck to arrive.

In the Rock Hill case, the scheme might have been successful if not for a misspelled street name, which prompted the post office to look up the woman’s address and forward it to her new residence, according to the station.

Police seized the pills, which they believe are counterfeit oxycodone from Mexico. Investigators are working to figure out who sent them and who was supposed to pick them up.