The fourth property of the serpent is that when it goes to a river to drink, it does not bring its venom along, but leaves it behind in its pit, so as not to poison the water. The interpretation says that when we go to the house of God we should leave behind the "venom" of wicked desire and anger toward others. This property of the serpent is usually second in the list.
The serpent in the van der Borcht copperplate engraving below is going toward water; there is no way to tell if it has left its venom behind.
The serpent in the woodcut below (from the Rome, 1577 edition) is traveling through a strange landscape toward the river.