Venom is different from poison although most people think they are the same thing. A poison is only toxic when the animal / plant is bitten or touched e.g. the poison dart frog, poison ivy, Death Cap Mushroom. A venom on the other hand is injected through devices such as barbs, tentacles or barbs into the recipient's tissues or blood stream and are only harmful when they reach there. As a consequence, snake venom will not affect you if ingested. However if you have any cuts in your mouth the venom could well find its way into your system. Venom is used to immobilise prey and can be used in self defence.
This is done using the LD50 test. This is the Lowest Dose that would kill 50% of a group of rodents (typically) mice (standard 20g ones) in a 24hr period. The most toxic venom would have the lowest LD50. A Black Mamba has an LD50 of 0.32mg i.e. 0.32mg of venom kills 500 grams of mice (it only kills half of those the venom is given to). Remember there are a 1000 milligrams in a gram! It is not correct to say that the snake with the lowest LD50 is the most dangerous. Other factors must be considered including: the natural aggressiveness of the snake, the amount of venom it can inject, the region where the snake lives e.g. black mambas have different toxicities in differing areas of Africa and the age of the snake. There have been lots of criticisms of the test: - for instance it does not consider the condition of the remaining 50% of the test e.g. some of the animals may not have died but could have brain damage / rodents might be more / less resistant to some poisons than humans are.
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