Well, it didn't exactly catch on fire but it was sparking!! I put some wet food (Natural Balance) in the microwave. I saw a spark but I thought I was seeing things. Then it started sparking some more! I stopped the microwave and when I took the plate out, the food was cinged and sizzling. I'm guessing there was a piece of metal in there but I couldn't find it. I'm so glad that I heat up her food because if I had given it to her straight from the can, she could have eaten a piece of metal.
I always check her food for any strange objects but now I'm even more paranoid.