Albert Barnes Commentary Job 20:16

"He shall suck the poison of asps: The viper`s tongue shall slay him." — Job 20:16 (ASV)

He shall suck the poison of asps - What he swallowed as pleasant nourishment will become the most deadly poison; or the consequence will be as if he had sucked the poison of asps. It seems that the ancients regarded the poison of the serpent as deadly, however it was taken into the system. They seem not to have been aware that the poison of a wound can be sucked out without injury to the one who does it, and that it is necessary for the poison to mingle with the blood to be fatal.

The viper’s tongue shall slay him - The early impression was probably that the injury done by a serpent was by its fiery, forked, and brandished tongue, which was supposed to be sharp and penetrating. It is now known that the injury is done by the poison ejected through a groove, or orifice, in one of the teeth. This tooth is made to lie flat on the roof of the mouth, except when the serpent bites, at which time it is elevated and penetrates the flesh.

The word “viper” here (אפעה 'eph‛eh), “viper,” is probably the same species of serpent that is still known among the Arabs by the same name—El Effah. (See the notes at Isaiah 30:6). It is the most common and venomous of the serpent tribe in Northern Africa and Southwestern Asia.

It is remarkable for its quick and penetrating poison. It is about two feet long, as thick as a man’s arm, beautifully spotted with yellow and brown, and sprinkled over with blackish specks. They have a large mouth, by which they inhale a large quantity of air, and when inflated with it, they eject this air with such force that it can be heard from a considerable distance. “Jackson.” Captain Riley, in his “Authentic Narrative” (New York, 1817), confirms this account. He describes the viper as the “most beautiful object in nature” and says that the poison is so virulent as to cause death in fifteen minutes.