Supernatural the book of monsters, demons, spirits and ghouls

Spirits, part 4

So that explains why reburial will work, at least sometimes. Why salt though? Folklore about our favorite mineral compound goes back thousands of years, and it's always represented purity. The Greeks, Romans, and Hebrews all sacrificed it, considered it powerful-and ate a lot of it. The Romans even salted their wine. We've known hunters who salt their beer-this comes from an old Scottish tradition in which a pinch of salt was added to a batch of mash to keep witches out of it. Romanian legend has it that pregnant women who don't eat salt will give birth to vampires. In Japanese folklore, troublesome ghosts are packed in jars of salt. Salt also symbolizes permanence, and the Old Testament refers to the "covenant of salt" between Yahweh and his wayward children. Scot's Discoverie of Witchcraft, from 1584, tells us that "the Devil loveth no salt in his meat."
And spirits loveth no salt blasted out of the barrel of a gun into their ectoplasmic mugs. It doesn't kill them, but it does get them out of your way for a while. It might also keep them out of your house if you place it along doorways and windowsills, but we've never seen that work for long.
Another trick we learned along the way is that most spirits and witches don't like iron. Our father had a theory that iron's magnetism has something to do with its power. We'll go along with that, but the important thing to us is that it works. And we're part of a long tradition of using it. Irish mothers used to put iron in their babies' cribs to prevent fairies or elves from switching the baby for a changeling; it's part of a bedrock of European folklore that witches can't pass over cold iron-and this one is true. We've seen it work. The Greeks and Romans kept iron out of their temples and cemeteries because they wanted spirits around and knew that iron would chase them away. Cold iron-iron that isn't smelted out of ore, but hammered pure without heating-is best, but any iron will do in a pinch.
Although there are some rules-spirits don't like iron, and they don't like salt, and they usually don't like us-beyond that, every spirit is a little different. Oh-also, they tend to smell of ozone, for reasons that we still haven't figured out. Here are some of the bad mofos we've run into over the past couple of years.