Answer:
I am heavy forward, but backward I'm not. What am I?
What gets bigger when more is taken away?
My teeth help me suck.
I walk on 4 legs in the morning 2 legs at noon and 3 legs at night.
A dragon's tooth in a mortal's hand, I kill, I maim, I divide the land.
It flows out of the soil, It burns you if it boils, And holds us in its coils, More valuable than gold, As black as it is old.