Teeth of every kind

Imagine living on a small farm in the country, long winter, and no money.  By the end of the year, you might live on a farm with toothless animals, and in that case, you might now have plenty of money to feed all those under your room.
In the Kingdom of Fable a magic is practiced called Rune magic. It has some similar elements to voodoo here. The main use of rune magic is warding. People get warded for things often such as a ward to be protected against fire.
Rune magic takes a lot of study and time to master. Spells are perfected over the course of generations with tiny tiny changes to make them longer in duration or effective or efficient. a spell example goes as follows
Protection from fire:

water collected from a spring under a full moon

pine needles collected on the longest day of the summer

red butterfly wing

a tooth from a purple spit dragon

Spells often have recipes that are oddly specific, but sometimes you can make do with small changes for an ok result. For example, this spell might work with everything remaining the same, except using pine needles collected just in the summer, and not on the longest day of summer. the spell would probably stay for less time and be less effective.
One thing that cannot be altered in a spell is the tooth type. Every spell has a tooth, making teeth an expensive and coveted item. Teeth are often worn on necklaces, keeping all sorts of teeth types and sizes handy at all times. No tooth, no rune magic, and that is the end of that.
Many animals wander the woods with fewer teeth then they should have. baring your teeth has been naturally selected out of the animals around this kingdom, most vicious animals scratch the ground and growl with their mouths closed.