What is so fragile that saying its name breaks it?

100 prisoners are stuck in the prison in solitary cells. The warden of the prison got bored one day and offered them a challenge. He will put one prisoner per day, selected at random (a prisoner can be selected more than once), into a special room with a light bulb and a switch which controls the bulb. No other prisoners can see or control the light bulb. The prisoner in the special room can either turn on the bulb, turn off the bulb or do nothing. On any day, the prisoners can stop this process and say "Every prisoner has been in the special room at least once". If that happens to be true, all the prisoners will be set free. If it is false, then all the prisoners will be executed. The prisoners are given some time to discuss and figure out a solution. How do they ensure they all go free?

I am the fastest animal but cannot climb the tree. What am I?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

A man was just doing his job when his suit was torn. Why did he die three minutes later?

What work can one never finish?

What is red and smells like blue paint?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

Can you name four days which start with the letter 'T'?