My mother was heating it to use as a hot-pack, and we were talking about something somewhat involving - which subject I have now entirely forgotten - and then smoke was pouring from the microwave. She pulled the towel out and threw it in the sink and ran cold water on it, but not before it put out more smoke that I thought possible from a hand-towel sized piece of cloth. I have to wonder if it wasn't treated fabric, or poly-cotton blend, or something, because this smoke is fouler than most anything I've encountered save burning plastic.
I was having trouble breathing for a while, and a damp washcloth helped some, but I'm still a little scratchy. Mom is fine, being about a foot shorter than I am gave her a big advantage for once. Nothing to call the siren-folks for; the disturbance was so mild Xiombarg didn't even bother to get up off my bed and hide. Adrenaline and excitement for me even so, whee. As far as I can tell, now everything is fine.