Next time you swim in Australia ask the lifeguard if there are any box jellyfish. These jelly fish can cause deadly cardiac arrest within minutes by punching holes in red blood cells and causing potassium to leak out of them. Scientists say the fasting-acting agent is a molecule called porin, which creates tiny ‘pores’ in red blood cells, allowing the potassium to leak out. Leakage of massive amounts from red blood cells is one of the worst things that could happen in the body. When the plasma potassium gets too high there’s no more electromotive force and the heart cannot beat.