Chest Monster/Real Life

Examples of Chest Monsters in Real Life include:

The old snake-in-the-can-of-nuts prank is a popular real life example.
The mata-mata, a South American variety of snapping turtle, does a variation on this; it sits perfectly still on the riverbed, with its mouth open and its tongue wiggling. When a fish comes to check out what it thinks is a nice worm to eat, the turtle swallows the fish.
The monkfish a species of flat angler fish that hides in the sea floor buried in the sand, it waves a lure to attract unsuspecting fish, and when it gets close enough it jumps out of the sand and gobbles it down.