There is a war going on between a certain tropical butterfly, Heliconius sara, and its only food source, the passion vine. This war involves chemical warfare. More precisely, the plant arms itself with cyanide bombs that are rather useful in getting rid of most insect pests. Not the case with the Heliconius saracaterpillar, though. This particular species of caterpillar is equipped with the means to disarm these bombs.
Certain cells in the passion vine's leaves contain cyanide linked to sugar compounds. Alone this compound of cyanide and sugar is harmless. But in nearby cells the plant possesses enzymes that when mixed with the cyanide and sugar can cause a release of poisonous cyanide gas. When most insects chomp down on a passion vine leaf the cells burst, releasing all of these chemicals so that they mix. Cyanide gas is formed, and the hungry insect dies.
How the heliconius caterpillar outsmarts the passion vine's attempt to poison it is not yet entirely clear to scientists. What they do know is that the caterpillar never comes into contact with the poisonous cyanide gas. In a chemical process not yet understood, the caterpillar replaces the cyanide molecule with a sulfur hydrogen molecule that is harmless. Thus, when the cell compartments burst there is no release of cyanide gas, and the caterpillar can go on feasting merrily.
This isn't the end of the war between the caterpillar and the passion vine, though. In the race to evolve new survival techniques, some passion vines have grown hooked hairs that they use to impale the bomb-disarming caterpillars.