Last week I microwaved some peanut butter M&Ms for 40 seconds, which is something I've done hundreds of times before to melt the chocolate on the inside. However, when I did it this time, there was some popping and then a big spark inside. There was no metal in the microwave, the bowl is microwave safe, but it did have a chip in it. I also left the M&Ms uncovered, while I usually cover them with a paper towel. Any idea what caused this? Someone elsewhere suggested this paper might be an explanation but I would think it would have happened before if that was the case.