Netflix’s The Witcher opens with an unforgettable scene where Geralt is fighting a Kikimore, and the first time the audience gets a proper look at his face, his eyes and blood vessels are black. The series failed to explained why this happened, as he looked pretty normal in the rest of the episodes, but the books have a proper explanation. The Witcher, based on the book series of the same name by Andrzej Sapkowski, was released on Netflix in December 2019, and was so well received it might be the platform’s biggest first TV season ever.

The Witcher is based on the books The Last Wish and Sword of Destiny, and follows Geralt of Rivia (Henry Cavill), an enhanced monster hunter known as a “witcher”; Yennefer of Vengerberg (Anya Chalotra), a powerful sorceress; and Princess Ciri (Freya Allan), who has powers of her own. Their stories are told separately and in different points in time, but their paths coverge at the end of the season. The world of The Witcher is very rich, with a number of human characters, monsters, mythical creatures and more, and one season wasn’t enough to explain everything.

Geralt’s first appearance left a big impression on viewers, who were left wondering why his eyes were black while fighting the Kikimore but not when he fought other creatures in subsequent episodes. Luckily, the source material (and the video games) has the answer.

The Witcher: How Geralt’s Eyes Turn Black

Over the course of season 1 of The Witcher, viewers witnessed a couple of battles between Geralt and different monsters, but it was only during his encounter with the Kikimore that his eyes were black and his facial expression was more aggressive than in the rest of the fights. This is because Geralt was under the effects of a potion, which are very common in the universe of The Witcher. Geralt has access to a number of potions and elixirs, which enhance different senses and abilities depending on what he needs.

Because witchers had to go through a mutation process in order to become stronger and faster so they can carry on with what witchers do, they are able to take potions and not die trying (as opposed to regular humans, who definitely wouldn’t be able to survive), and instead enjoy the benefits they bring. The black eyes are his pupils completely dilated, allowing him to see better in the dark, which fits with the scenario in the opening scene of the series. Potions can also enhance speed, endurance, healing, and more, depending on what they need to fight each monster. With more monster hunters joining The Witcher in season 2, it’s possible the series will explore potions a bit deeper in the near future, allowing those not familiar with the books and video games to better understand what witchers can do.