The pork experts who guided us said that if an apple was put into the suckling pig's mouth before roasting, it would quickly turn to a texture more like apple sauce than an apple. The pristine apple is put into the pig's mouth after it is removed from the spit.So the apple is purely a decorative item.
Suggestion has it that place a small block of wood into the pig's mouth before roasting to brace it so an apple can be inserted later. Cranberries or cherries are often used in the eye sockets and some people like to give the pig a collar of cranberries, parsley or flowers.
The poor pig, whose very name conjures up filth and sweat in common parlance, is subjected to even greater indignities before it is consumed.
http://en.wikipedia.org/wiki/Pig_roast
