The other five species of venomous snakes that occur in Arkansas have hemotoxic (=hemolytic) venom with proteins that break down tissue following injection into another animal. This venom facilitates capture of the snake's mammalian prey. These venomous snakes have another trait in common, a vertically elliptical pupil (this resembles a cat eye - see top photo of a copperhead). By contrast, most non-poisonous snakes have a round pupil, such as the black rat snake ( Elaphe obsoleta - bottom photo). Note: the coral snake also has a round pupil.
In addition, these five venomous snakes are known as "pit vipers." The pit is located between the nostril and the eye (the dark triangle in the top photo) and houses a heat-sensing organ, which allows pit vipers to "see" into the infrared portion of the electromagnetic spectrum. Infrared wavelengths are invisible to humans. With the aid of this heat-sensing pit, pit vipers locate rodents even at night (the heat given off by the rodent can be "seen" by the snake).