Many fruits and other plant foods contain compounds that have the potential to release cyanide. These compounds are usually glycosides - i.e. they consist of a sugar molecule linked to a cyanide group, usually indirectly through another component.
The release of cyanide from these compounds occurs by enzymic hydrolysis, usually when the plant tissue is crushed or otherwise disrupted (allowing the active enzyme to reach the substrate), but it can also occur in the digestive system after the food has been eaten.
Cyanogenic glycosides occur in many food plants like cassava, lima beans, and the seeds of some fruits-- peaches, for example. Because of their cyanide content, ingestion of large amounts of cassava and, to a lesser extent, lima beans can be fatal if these foods are eaten raw or are not prepared correctly.
The toxic potential of cassava has been known for hundreds of years, and traditional methods of food preparation from cassava have been developed to reduce cyanide content. These include leaching out the linamarin precursor, washing in running water before cooking (bruising of the cassava root during harvesting often results in considerable cyanide release), and boiling in uncovered pots, so that the cyanide can evaporate. Fermentation steps also significantly reduce cyanogenic potential. The risk of food poisoning from cassava can be reduced by avoiding bruised or non-fresh material, and avoiding roots known to be bitter.