background knowledge
The jellyfish " senses " whether the touch is for another tentacle, for prey, or for an enemy like humans. Human skin secretes a substance to which the stinging cell receptors respond. This information is passed on to the nettle capsule by messenger substances.
Then something amazing happens in the capsule: In a fraction of a second, the enormous pressure of 150 to 200 atmospheres is created – 200 times the air pressure of a car tire. The coiled microprojectile in the stinging capsule is fired at 40,000 times the acceleration of gravity. This "kiss of the Medusa" is one of the fastest movements that have ever been observed in nature. Like a high-velocity projectile, the harpoon penetrates the stratium corneum, the tough stratum corneum of the skin, and the jellyfish venom enters the bloodstream .