3. Castor beans
Many a granny came armed with a spoonful of castor oil to heal all ills, and studies show that it does indeed have health benefits to offer. Just be sure not to eat the beans from which the oil came. If castor beans are chewed and swallowed, they can release ricin, one of the most toxic poisons known to man. Eating just one or two castor beans can easily cause the demise of the eater. Ricin has been investigated as a warfare agent, and has even been employed by secret agents and assassins.