Answer:
I build up castles. I tear down mountains. I make some men blind. I help others to see.
What has a big mouth, yet never speaks?
The more of them you take, the more you leave behind. What are they?
As I walked along the path I saw something with four fingers and one thumb, but it was not flesh, fish, bone or fowl.
Though blind as well, can lead the blind well.
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.