Answer:
A leathery snake, with a stinging bite. I'll stay coiled up, unless I must fight.
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.
I am a box that holds keys without locks, yet they can unlock your soul.
The man who made it didn't need it. The man who bought it didn't use it. The man who used it didn't want it.
Until I am measured I am not known, Yet how you miss me when I have flown.
What did the piece of wood say when he saw the screwdriver and screws approaching?