Pits or seeds of apples, mangos, peaches, pears or apricots
Although it would take at least a cup of these ground seeds to poison someone, seeds from apples, mangos, peaches, pears and apricots contain a chemical that can turn into organic cyanide.
Wild mushrooms
Mushrooms contain a host of beneficial properties including antioxidants, B vitamins and potassium, according to Healthline. Some doctors note, however, that heat is required to release some of these nutrients and benefits. Plus, raw mushrooms are known for being hard to digest, and they are among the most concentrated sources of a naturally-occurring toxin, agaritine. Various studies and research found in some rat studies that agaritine has a carcinogenic effect. That said, cooking destroys these compounds so you can still safely eat the cooked variety.