Feet
Front foot. The 5 digits make a 1-3-1 pattern.
Hind foot. Note the opposing thumb. It looks much like an infant's hand.
Tracks
You will scratch your head when you encounter the tracks of an opossum for the first time. The opposing thumb of the hind foot helps make the tracks very distinctive.
Gait
An alternating stride, sometimes with tail drag, with indirect register mark the
opossum. 
