'Cancer cells contain an enzyme that is not found in healthy cells, beta-glucosidase. This enzyme “unlocks” the amygdalin compound, releasing the deadly toxins within the cancer cell. Only cancer cells metabolize amygdalin. Healthy normal cells don’t.
Most non-cancerous cells contain another enzyme, rhodanese. The few free cyanide molecules that may conceivably escape are bound to sulfur molecules by rhodanese, creating harmless cyanates that are eliminated in the urine. Safe enough?'