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Snakes may deliver such a "dry bite" rather than waste their venom on a creature too large for them to eat, a behaviour called venom metering.Even without venom, some snakes, particularly large constrictors such as those belonging to the Boidae and Pythonidae families, can deliver damaging bites; large specimens often cause severe lacerations, or the snake itself pulls away, causing the flesh to be torn by the needle-sharp recurved teeth embedded in the person.
As open grasslands replaced forested areas in parts of the world, some snake families evolved to become smaller and thus more agile.Venom is composed of hundreds to thousands of different proteins and enzymes, all serving a variety of purposes, such as interfering with a prey's cardiac system or increasing tissue permeability so that venom is absorbed faster.Venom in many snakes, such as pit vipers, affects virtually every organ system in the human body and can be a combination of many toxins, including cytotoxins, hemotoxins, neurotoxins, and myotoxins, allowing for an enormous variety of symptoms.Earlier, the venom of a particular snake was considered to be one kind only, i.e.either hemotoxic or neurotoxic, and this erroneous belief may still persist wherever the updated literature is hard to access.For example, in the United States, about seven to eight thousand people per year are bitten by venomous snakes (about one in 40 thousand people) and about five people die (about one death per 65 million people).
Television, literature, and folklore are in part responsible for the hype surrounding snakebites, and people may have unwarranted thoughts of imminent death.
In the Middle East it is carpet vipers and elapids.
In Central and South America it is snakes of the Bothrops and Crotalus types, the latter including rattlesnakes.
They often happen when a person steps on the snake or approaches it too closely.
In the United States and Europe snakebites most commonly occur in those who keep them as pets.
Infection is often reported with viper bites whose fangs are capable of deep puncture wounds. Most snakebites, whether by a venomous snake or not, will have some type of local effect.