What Am I Riddles

Question: After you go through a fall I will take over.All life will stall, or at least grow slower.What am I?

Question: Countless blades that bend with a touch,
exploited by kids who want to make a buck.

What am I?

Question: What has four legs and can't walk?

Question: I am a big threat to humanity,
but you wouldn't get rid of me even if you could.

What am I?

Question: At the end of a long dark cave there is a monster made of lead. Be careful. One twitch of the finger and you will release it.

What is it?