Answer:
Weight in my belly trees on my back nails in my ribs feet I do lack.
I am easy to see but no one likes looking at me. Without me there would be no you. I can make you complain or make you happy. But you almost always take me for-granted.
I am perfect with a head perfect without a head; Perfect with a tail perfect without a tail; Perfect with either neither or both.
I am the kind of food monkey likes and people slip on me and fall in cartoons.
I can't go left, I can't go right. I am forever stuck in a building over three stories high. What am I?
A little house full of meat, no door to go in and eat.