Josie had spent the better part of the morning barking at the mailbox. That was puzzling; usually she was easygoing and mild-mannered. I figured whatever she was trying to tell me, it wasn't that we had mail.

The lid was down and the box was wide open. I put Josie in the house, tiptoed back and peeked inside. Crouched atop a Publisher's Clearinghouse entry was the biggest possum I'd ever seen.

I armed myself with a garden rake and implored it to depart forthwith. When it refused to budge, I gave it a little poke with the handle, hoping it would climb down and shuffle off without fanfare, or maybe "play possum," as possums do when they don't like the odds.

Instead, snapping and snarling, it tumbled from the box and darted under the house.

While they rarely invade mailboxes, it's not at all uncommon to encounter a possum in the suburbs. They usually hide out during the day, but roam freely after sunset, feeding on plants and small animals.

Although they have the smallest brains-relative to body size-of any North American mammal, they're brilliantly adaptable and manage to thrive even in the city. What they lack in cranial capacity they make up for in dentition; possums have 50 teeth, more than any other land mammal in the U.S. They also have prehensile tails; and they're America's only marsupial, raising their young in a pouch on the mother's belly.

A week or so later, I came home late from a trip. As I climbed the front steps in the dark, something grabbed my pants cuff. I ran to the car, and flicked on the headlights, just in time to see it-or one just like it-vanish under the porch.

The next day I sprinkled mothballs under the house. That seemed to do the trick; no possums made a return call. I also sent in the Publisher's Clearinghouse entry-they didn't call back, either.