The Collaborative International Dictionary
To act possum
Possum \Pos"sum\, n. [Shortened from opossum.] (Zo["o]l.) An opossum. [Colloq. U. S.]
To play possum, To act possum, to feign ignorance, indifference or inattention, with the intent to deceive; to dissemble; -- in allusion to the habit of the opossum, which feigns death when attacked or alarmed.