This expression's meaning may be guessed from the words in it, so it is not an idiom. To play possum is to deceive an attacker by pretending to be dead or vanquished, as the possum proverbially does.
i think its a possum
The Leadbeaters possum eats tree sap of wattle and eucalyptus trees.
a possum
Avril Lavigne plays Heather the teenage possum on Over the Hedge.
you possum.
Georgia's state possum is the POGO possum
Properly called the opossum. Commonly called a possum.
There are several:Tree-kangarooKoalaPossum, e.g. Ringtail possum, Brushtail possum, Honey possum, Leadbeater's possum, Pygmy possum, etcOpossumQuollPhascogaleSugar gliderFeathertail gliderSquirrel gliderGreater gliderMahogany gliderYellow-bellied gliderCuscus
you possum.
There is no such thing as a merino possum. However, "possum merino yarn" is a blend of possum fur and fine Merino wool, made in New zealand, where the possum is an introduced pest.
The singular form of the word "possum" is possum. The plural is possums.