Opossum, to thee I opine!

O is for oscilating ears that move back and forth to hear,
P is for picky, which we know you aren't at all,
O is for omnivore because you like to eat all manner of plant and critter,
S is for silly because you're a funny looking fellow,
S is for 'stay back!' when you gap your mouth open and show your teeth,
U is for ugly, for some people think,
M is for marsupial, the most interesting animal here by far!

How I do enjoy opossums!