Answer:
My teeth are sharp, my back is straight, to cut things up it is my fate.
What goes in, but never through? I've got some and so do you. We might lend one, or even two, but only if our trust is true.
Thousands lay up gold within this house, But no man made it. Spears past counting guard this house, But no man wards it.
What letter comes next: O T T F F S S ?
Of these things - I have two. One for me - and one for you. And when you ask about the price, I simply smile and nod twice.
What is yours but only used by others?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?