It’s not unusual to see the occasional rat or mouse in the subway, usually darting across the tracks. However, I once saw a squirrel who had gotten into Battery Park subway station (most likely from the park). He bounded down the Third Rail for several yards, a masterful balance beam performer. All went well until he paused, sat up on his hind legs, and his tail went down and touched the trackbed, thereby completing the electrical circuit…and killing the squirrel by electrocution.