Answer:
Nothing specific, but more than a few. This many clustered, together will do.
What flies forever, rests never?
What always comes into the house through the keyhole?
How many bricks does it take to complete a building made of brick?
What has one head, one foot, and four legs?
I am the fountain from which no one can drink. For many I am considered a necessary link. Like gold to all I am sought for, but my continued death brings wealth for all to want more.