Wiktionary
play possum
vb. 1 (context idiomatic English) to feign death; to remain quiet and still to escape attention or remain undetected; to lay low. 2 (context idiomatic English) to feign sleep, illness, etc. 3 (context idiomatic dated English) to dissemble or to feign ignorance; to disguise or conceal something in order to deceive.
WordNet
play possum
v. to pretend to be dead
Usage examples of "play possum".
Popeye, who could play possum just as well as Possum could, pretended to be asleep again, and Possum pretended he didn't care what happened to the dog.
Longarm thought of calling out, but it would be just like Shaw to keep still and play possum.
For an instant he had an impulse to switch off the reading lamp, or at least play possum and pretend that he hadn’.