Spilled salt
In the Middle Ages in the UK, salt was a very expensive commodity, witnessed by the expression that someone was "worth his salt" i.e. he was of sufficient standing in the household to "sit above the salt" and be entitled to make use of it. The lower orders sat "below the salt" and were forbidden to enjoy it.
Thus, the supersttion arose that spilling the salt was a harbinger of bad luck, the only remedy for which was to scoop up a pinch of the spilled material and throw it over your left shoulder, in order to blind the Devil who was permanently stationed there to pounce on you whenever you were less than righteous.
Spilled salt
In the Middle Ages in the UK, salt was a very expensive commodity, witnessed by the expression that someone was "worth his salt" i.e. he was of sufficient standing in the household to "sit above the salt" and be entitled to make use of it. The lower orders sat "below the salt" and were forbidden to enjoy it.
Thus, the supersttion arose that spilling the salt was a harbinger of bad luck, the only remedy for which was to scoop up a pinch of the spilled material and throw it over your left shoulder, in order to blind the Devil who was permanently stationed there to pounce on you whenever you were less than righteous.