Answer:
My sides are firmly laced about, Yet nothing is within; You'll think my head is strange indeed, Being nothing else but skin.
A seed am I, three letters make my name. Take away two and I still sound the same.
Twigs and spheres and poles and plates. Join and bind to reason make.
I cost no money to use, or conscious effort to take part of. And as far as you can see, there is nothing to me. But without me, you are dead.
What can be heard and caught but never seen?
People take me on walks and I run and have fun. What am I?
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?