Some plant food has natural poisons and they include:

Potato: The green part in potato contains solanine, a nerve toxin. In high concentration the symptoms are vomiting, diarrhoea, headaches and even paralysis of the central nervous system.

Green beans: The poison in raw green beans is called lectin phytohaemagglutinin. Ten minutes boiling degrades this toxic component.

Note: Sprouts of pulses are rich in haemagglutin and should not be eaten too much. Haemagglutin is a substance which causes red blood cells to clump together.

Beetroot and Asparagus: The natural poison in these vegetables is saponin. If it is injected, like all soaps, it damages the blood cells and is thus highly toxic. But it is the property of the whole molecule, but on oral intake, hydrolysis readily occurs in the mouth, splitting it into its sugar moiety and sapogenin and it is quite safe. Now you know why we have to grind the meal 32 times in our mouth.

Lakritz: Lakritz, licorice contains glycyrrhizin which metabolizes in our body to glycyrrhizin acid. It changes the mineral household and causes the problems of high blood pressure, water collection in the legs and muscle weakness. Healthy persons can eat a maximum of 50g and children and pregnant women can eat much lower than this.

Bitter almond: Its natural poison is amygdaline. It can be broken down into the poisonous substance hydrocyanic acid (cyanide).