by M. Kathy Raines Mouth agape, tongue sticking out and fur matted, the possum lay stiff and motionless. Its victor, a lab mix, grinned excitedly, but the dog, like many carnivores—especially well-fed ones— has scant interest in gnawing a creature that won’t play along.  “C’mon, possum, you can do it!” I cheered, bundling the dog…