Why Do Green Beans Spark In The Micrwave I Put Some Cooked Green Beans In The Microwave And They Sparked???!!?

I put some cooked green beans in the microwave and they sparked???!!? - why do green beans spark in the micrwave

I can not imagine metal in the beans and I wonder why it broke. I cook in a nonstick pan last night and just add a little salt, no butter. Could the salt caused the spark?