The Box Jellyfish is possibly the world's most deadliest jellyfish. The most dangerous of all these species of these advanced jellies is the tiny Irukandji. Irukandji is no bigger than a man's finger, but what it lacks in size, it has a sting that would make Mr. T cry like a baby. To make matters worse, there is no antidote. Irukandji has a venom that can work in seconds. Irukandji's sting can cause severe pain all over the body, headaches, nausea, sweating, vomiting, high heart rates and blood pressure, and you're pretty much dead after that. But Irukandji just might have shown big things can come in small packages.