Answer:
It is something you will never see again.
Consuming food would be pretty tough without these chompers
What can be any size or shape and gets bigger the more you take from it?
Sitting down you have it, Standing up you don't.
What grows when it eats, but dies when it drinks?
Though not a plant, has leaves. Though not a beast, has spine. Though many wouldn't need this thing, It's more valuable than wine.