The Trial of the grasses or herbs was an incredibly painful trial which young witcher apprentices were subjected to. It required the consumption of special alchemical ingredients known as "the grasses" and affected the nervous system. Reportedly, only three in ten survived the trial, those who didn't survive died in agony, but those who did gained lightning quick reflexes, their signature cat-like eyes, and other bodily enhancements in return. The trial was performed in the witchers' laboratory at Kaer Morhen. Though another lab can be found outside the castle and inside a cave to the south, in Witcher 3 Wild hunt, the player can explore this lab during the scavenger hunt for Wolf School gear and Geralt will reminisce about his past subjection to the chemicals.
- In the video game, it is during this trial that Geralt's hair is said to have turned completely white. In the books, however, Geralt's hair turned white as a side effect of some "additional experiments" which were performed on him. However both are true due the fact that the ones experimenting on Geralt modifed his traits.
- "Trial of the Herbs" is the title of a song by Marcin Przybyłowicz included on the Inspired by The Witcher CD.