Perforation of the alimentary tract by a foreign body is quite rare, even if said foreign body is a bone. Fish bones are commonly swallowed.
People with removable dentures, however, lack much of the tactile sensation when chewing food, which is how a chicken bone can accidentally be swallowed as well. Perhaps the leading culprit is the chicken's fibula, a thin, sharp bone.
Strangely enough, in the case presented here, the thicker edge of the bone perforated the esophagus, not the sharp edge (scroll and see for yourself). The bone was carefully extracted and was indeed the notorious fibula.