The first property of the serpent is that when it grows old its eyes become dim. To become young again the serpent fasts for forty days until its skin loosens, then it crawls through a narrow crack in a rock to shed its old skin and become new again. The interpretation is that the "spiritual man" must go through the narrow way of abstinence and tribulation to shed his old life and become new again.
The serpent in the van der Borcht copperplate engraving below is shedding its skin as it crawls through a hole in the rock. The serpent has distinct ears, a feature commonly found in bestiary illustrations.
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The woodcut below (from the Rome, 1577 edition) also shows the serpent shedding its skin.
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Properties of the Peacock
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