Answer:
The more of it there is, the less you see.
I am free for the taking. Through all of your life, though given but once at birth. I am less than nothing in weight, but will fell the strongest of you if held.
My teeth are sharp, my back is straight, to cut things up it is my fate.
A red drum which sounds without being touched, and grows silent, when it is touched.
Hard to catch, easy to hold. Can't be seen, unless it's cold.
I have two eyes in the front and a lot of eyes on my tail
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?