The micronutrient essential to the production of thyroid hormone is the halogen Iodine.

It will "hurt" (or kill, rather) cows and dogs if they are exposed to a lot of it, but otherwise it is a good fertilizer, micromineral supplement, topical/oral treatment for certain ailments, and an insecticide and fungicide.

No. This is a myth that has been passed along by drug addicts that have been trying to find unique ways of getting the necessary ingredients for illegal drugs like methamphetamine, also commonly known as crystal meth.