What're the two body systems opossums use to fake their death?

Apparent death, colloquially known as playing dead, feigning death, or playing possum, is a behavior in which animals take on the appearance of being dead. This form of animal deception is an adaptive behavior also known as tonic immobility or thanatosis. Apparent death can be used as a defense mechanism or as a form of aggressive mimicry, and occurs in a wide range of animals.

When induced by humans, the state is sometimes colloquially known as animal hypnosis. According to Gilman et al.,[1] the investigation of "animal hypnosis" dates back to the year 1646 in a report by Athanasius Kircher.