Venomous snake
Belcher's sea snake ("Hydrophis belcheri"), which many times is mistakenly called the hook-nosed sea snake ("Enhydrina schistosa"), has been erroneously popularized as the most venomous snake in the world, due to the first edition of Ernst and book, "Snakes in Question: The Smithsonian Answer Book", published in 1996.
Prominent venom expert Associate Professor Bryan Grieg Fry has clarified the error: "The hook nosed myth was due to a fundamental error in a book called "Snakes in Question". In there, all the toxicity testing results were lumped in together, regardless of the mode of testing (e.g., subcutaneous vs. intramuscular vs. intravenous vs. intraperitoneal). As the mode can influence the relative number, venoms can only be compared within a mode. Otherwise, it's apples and rocks." Belcher's sea snake's actual LD (recorded only intramuscularly) is 0.24 mg/kg and 0.155 mg/kg. Studies on mice and human cardiac cell culture show that venom of the inland taipan, drop by drop, is the most toxic among all snakes.
Venom
Some 450 species of snake are venomous. Snake venom is produced by glands below the eye (the mandibular gland) and delivered to the victim through tubular or channeled fangs. Snake venoms contain a variety of peptide toxins, including proteases, which hydrolyze protein peptide bonds, nucleases, which hydrolyze the phosphodiester bonds of DNA, and neurotoxins, which disable signalling in the nervous system. Snake venom causes symptoms including pain, swelling, tissue necrosis, low blood pressure, convulsions, hemorrhage (varying by species of snake), respiratory paralysis, kidney failure, coma and death. Snake venom may have originated with duplication of genes that had been expressed in the salivary glands of ancestors.