Cyanide can be in the form of a colorless gas or a crystal, but either way, it's pretty deadly. It smells like bitter almonds, and exposure to cyanide can cause symptoms such as headache, nausea, rapid breathing and heart rate, and weakness in just minutes. If untreated, cyanide kills by basically depriving the body's cells of oxygen. And yes, it can be made from apple seeds, but don't worry if you eat a few. You'd need to eat about ten apple cores before there was enough cyanide in your system to have an effect. Please don't do that.