Why does tuna spark when heated in a microwave?

Question

I've noticed that sometimes canned tuna (no, not still in the can but in a bowl or plate) will produce sparks or arcing after just a few seconds in the microwave. Is there something metallic in the tuna that causes this or is it something else?

Answer 1

I put sone tune on a microwave safe dish and for the first 2 or 3 seconds it was sparking the same way metalic trim on glassware does. Is it that loaded with mercury or maybe metal particles from the processing plant?