Pregnant every time you see her, yet she never will give birth.
What's as small as a mouse but guards a house like a lion?
I am nothing really at all, Yet I am easily found; Ignore me at your own peril, and you might end up crowned!
A hill full, a hole full; yet you cannot catch a bowl full. What is it?
I am believed to be only one dimensional, and tinier than anything can be, and there are many who say that I am the basis of all that we see. What am I?
Man's most important invention.