Answer:
This only turns over once you have traveled very far. What is it?
I have a tongue, but do not talk. I follow close, but neither run nor walk. Coupled and hitched, but never married. You couldn't bear the load I've carried.
Metal or bone I may be, many teeth I have and always bared. Yet my bite harms no one. And ladies delight in my touch.
To unravel me you need a simple key, no key that was made by locksmith's hand. But a key that only I will understand.
What kind of nut is empty at the center and has no shell.
Almost everyone needs it, asks for it, gives it. But almost nobody takes it.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?