The Trial of The Grasses was a painful process that used a mysterious mixture of plants, elixirs, and other unknown ingredients to modify the physiology of young witcher adepts to make them fully fledged witchers in terms of reflexes and heightened senses. However, this process caused so much strain on an adept's body, only about 3 to 4 out of every 10 adepts survived, with the rest dying in agony.