I am not ignorance; I am choice. I see the door and swear it isn’t there. I survive only while you look away. The moment you name me, I begin to die. What am I?

I guard your treasures, yet have no eyes, I click and I turn where your secret lies. A twist of numbers, a key to my heart, open me wrong, and I won’t part.

Echoes of a quartet, multiplied force, a leap from pair to foursome, fourfold strength in a single course.

I'm spoken through problems, some yet to be solved. Through logic and science, I'm always involved. Most everyone knows me, some animals too. I help you determine what's many, what's few.

We are very little creatures; all of us have different features. One of us in glass is set; one of us you'll find in jet. Another you may see in tin, and a fourth is boxed within. If the fifth you should pursue, it can never fly from you. What are we?