needle
the eye of a needle: seeeye.
get the (dead) needle become very annoyed. British informal
a needle in a haystack something that is almost impossible to find because it is concealed by so many other similar things.
2002New York Times Magazine Terrorists don't fit a consistent profile: you're looking for a needle in a haystack, but the color and shape of the needle keep changing.
sharp as a needle: seesharp.