This pet has wandered or fell into a situation where it has become trapped and cannot get out. The most common of these is the dog that wanders into the neighbor's garage or shed while the door is open and then becomes trapped when the unknowing neighbor closes the door.
Dogs have been known to become trapped in sheds, storm drains, outhouses, abandoned buildings and even a discarded kitchen cabinet. We had one long haired spaniel that became trapped in a brier bush two blocks from home. She stayed quietly in the bush for five days until she was found.
This possibility should always be looked into when a pet that normally has outdoor access does not return as usual and there is a nuisance danger that could encourage this situation. Also when a dog goes missing with a leash or tether on.