By Carlos AndradeWed Jun 22, 8:48 AM ET Before the arrival of Spanish colonizers some 500 years ago, Indians in what is now Ecuador dipped their arrowheads in venom extracted from the phantasmal poison frog to doom their victims to convulsive death, scientists believe. More recently, epibatidine -- the chemical which paralyzed and killed the Indians' enemies -- has been isolated to produce a pain killer 200 times more powerful than morphine, but without that drug's addictive and toxic side effects. Pharmaceutical companies have not yet brought epibatidine to market but hope to discover other chemicals with powerful properties in...