Cone snails are predatory marine mollusks specializing in the paralyzing venom of instant action. Person won’t suffocate directly from it, but he can drowning accidentally, getting a dose.
Dart frogs are famous for both its beautiful bright colors, and the most dangerous poison - batrachotoxin. They directly attack the heart muscle causing arrhythmia and cardiac arrest. Antidotes to it does not exist, although it’s hard to poison in such a manner.
Irukandji jellyfish is very insidious - it does not exceed the size of 25 millimeters, and its bite is almost imperceptible. The action of its venom resembles a strange disease, that’s why it has received the name "Irukandji syndrome". After such a "delightful" syndrome as persistent vomiting, pulmonary edema and monstrous pain throughout the body, either healing or death occurs.
Pitohui dichrous is a very beautiful and terribly poisonous bird from New Guinea, receiving batrachotoxin from bugs it eats. Pitohui is harmless to humans, but it is not recommended to take it in the hands - you can suffer burns.
The blue-ringed octopus with the threat of life can reward the offender poisonous bite, leading to almost momentary paralysis and death. Recently it was found out that the toxic poison is produced by symbiotic bacteria in the saliva of the mollusk.