Question: If you throw me out of the window,
I'll leave a grieving wife.
Bring me back, but through a door,
You'll see someone giving life.
What am I?
Answer: The letter 'n'.
Taking 'n' out of 'window' creates 'widow'. Putting 'n' into 'door' creates 'donor'.
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?
Answer: I'm a mirror.