What Am I Riddles

Question: What cannot be seen or felt, but can only be broken by voice?

Question: I can be half without getting thinner.
I can shine with no fire.
I can be hidden but never taken.
I can stay dry while moving the ocean.

What am I?

Question: My thickness is no more than a few centimeters, yet my depth can span to infinity. Although mundane, I intimidate most animals. When in my presence, you will inevitably follow me. What am I?

Question: I stare at you, you stare at me.I have three eyes, yet can't see.Every time I blink, I give you commands.You do as you are told, with your feet and hands.What am I?

Question: Tear one off and scratch my head. What once was red is black instead. What am I?