From the drsfosterand smith website "Behavior/Interaction: Shy and solitary, they should only be handled for short amounts of time. When startled or threatened, they may puff up with air and hiss. They may also curl into a ball and "play 'possum" as they darken in color. It takes considerable time for them to feel secure enough to uncurl and move about afterwards." (This paragraph pertains to veiled chams)
From scienceray.com " Serious defenses are needed when you’re tiny and at the bottom of the food chain. The leaf chameleon has a couple of interesting defense mechanisms if its camouflage doesn’t deter predators. First, it will close its eyes to remove all source of movement. If the branch the chameleon is on shakes, the chameleon will promptly drop like a dead twig into the leaves below and play possum. If the predator is unusually persistent and manages to grab the chameleon, the reptile will vibrate! "(This paragraph pertaind to leaf chams.)
From
http://www.altaranchopet.com/Information_library/reptile_handouts/chameleon_care1.htm
BEHAVIOR AND PHYSICAL CHARACTERISTICS
STRESS
Veileds are shy in nature, and should be kept visually separate until breeding age (5 months). When startled or feeling threatened by another Veiled, they may drop to the floor of the enclosure, curl into a tight fetal position, darken and color, and "play possum." Like opossums, it takes a considerable time until they feel secure enough to unfold and begin moving about again. Changing or rearranging the furnishings in the cage can cause stress; try to plan ahead and reduce the need for change. "
These are just a few of the sites that talk about chams playing possum. A little RESEARCH will go a long way
Bob