Green Beans

I was warming up some green beans for Jimmy this afternoon (woohoo, he’s eating green beans!) and was surprised to see them start sparking in the microwave. I pulled out the beans and examined them for foreign objects, but found nothing out of the ordinary, save a couple of black dots on two of the beans. What in the world? Why did they cause the microwave to go nuts? I searched the web for others who have experienced this phenomenon and found some interesting info. Apparently, green beans are a dense vegetable that has higher amounts of minerals, which can act like metal in the microwave. Has anybody else ever had this happen to them? I’ve been microwaving green beans for a while now (sorry mom, I use whatever dish is at hand, even if it’s *gasp* plastic), and this is my first fireworks show.