Possum

We were walking along in lower Allston at night, and a sound came from the left. We looked over and up, and suddenly we had jumped into the street. We'd been walking alongside a chainlink fence, and perched atop it, a bit above our heads, was a possum. The sound must have been its tail jangling against the fence. The possum is a terrifying and ugly animal. We stared at it and it looked back still calmly and ominously sitting atop the fence.

In a few moments we walked along, continuing our walk. A guy crossed paths with us. We realized that in a minute or so he would pass by the possum. We waited, looking after him, and suddenly saw him jump to the street and start running, not even looking back I think.