Has your GS come into contact with anyone who has arthritis or was in need of a heating pad? Dried corn filled bags (dried beans and rice work too) are all the rage now. You warm them in the microwave and they retain heat like a hot water bottle. the type corn used is a different type then popping corn but I wonder if he saw someone using a corn bag and that is how he got the idea.
http://www.warmhugs.com/
http://www.cornwarmerz.com/faq-page
http://www.wikihow.com/Make-Corn-Bags