Difference between Sharp as a needle and Sharp as a wet noodle

sharp as a needle—(also: sharp as a razor) very intelligent; quick to learn or realize things:

• The child was as sharp as a needle and soon began to use quite difficult words.

sharp as a wet noodle—(U.S. ironic) very dull, stupid:

• You can tell from the things he says that he’s about as sharp as a wet noodle.