It started moving, on its own, a few hours after it was left.
The package was freaking out the workers, said postal inspector David McKinney.
Figuring it was an animal, McKinney wanted to find the sender and explain what animals could and could not be mailed. But whoever posted it, didn't want to be found, giving a fake name and a bad address.
McKinney had no luck contacting the recipient, either, so he got a search warrant and opened the package. It turned out to be a ferret, along with some food, toy cars and a doll.
Ferrets are illegal in Puerto Rico.
The one-pound ball of fur was taken to an animal shelter and put up for adoption. Workers there named him "Stamps," and the operator of a ferret shelter adopted him.
McKinney said he's just glad it wasn't a snake. Someone mailed an eight-foot python from the same post office a few years ago, and it slithered out of its package while in transit.