An octopus small enough to sit in your palm carries no antidote to its own bite

The blue-ringed octopus, barely the size of a golf ball, carries tetrodotoxin, the same nerve poison found in pufferfish, potent enough to kill an adult human within minutes through paralysis and respiratory failure. Its warning display, rings of electric blue that flare when it's threatened, is one of the clearest visual danger signals in the animal kingdom. No antivenom exists; survival depends entirely on artificial respiration until the toxin clears.

— Wikipedia contributors, Blue-ringed octopus — genus Hapalochlaena