Hydrogen peroxide

When threatened, the bombardier beetle fires hydrogen peroxide and hydroquinone from a reservoir into a reaction chamber, where enzymes trigger an explosive reaction that heats the liquid to nearly 100°C. It blasts this scalding, pressurized spray at predators in precise aimed pulses.

Sealed honey essentially never spoils. Its water content is low (~17%) and bound to sugar, its pH of 3–4.5 is acidic, and bee enzymes add hydrogen peroxide. Microbes can't survive, so millennia-old honey is found unspoiled in Egyptian tombs.