What did the author of Proverbs admire the snake for?

In Proverbs 30:18-19, the author tells of the things he finds most beautiful and inspiring: "There be three things which are too wonderful for me, yea, four which I know not: The way of an eagle in the air; the way of a serpent upon a rock; the way of a ship in the midst of the sea; and the way of a man with a maid."

The purpose of listing these beautiful and inspiring things was to then compare them with four things he finds despicable: a servant who reigns, a fool who is satisfied, an odious woman when she is married and a servant girl who inherits her mistress' property.