The nocturnal marsupial famous for “playing dead” is the opossum, especially the Virginia opossum in North America.
The Virginia opossum, Didelphis virginiana, is a solitary, mostly nocturnal animal found from southern Canada through Central America. When threatened, it may enter an involuntary state of tonic immobility: it collapses, becomes limp, and appears dead rather than actively fighting or fleeing.
This defense can last for several hours. The animal may lie on its side with its mouth open, tongue extended, and eyes partly closed; it can also release a foul-smelling fluid. The behavior inspired the expression “playing possum,” although the response is more like an automatic physiological shutdown than a conscious performance.
“Possum” and “opossum” can cause confusion. The Virginia opossum is the North American animal usually meant by “opossum,” while Australian possums are different marsupials. Opossums are also not rodents: they are marsupials, and females carry their young in a pouch.