In an interview with IGN at San Diego Comic-Con, Henry Cavill shared details about Netflix’s The Witcher, including how magic is used throughout the show and what that last scene was about in the trailer.
In terms of how magic will be portrayed in the series, Cavill explained, “The thing with magic as well, its one of those things which we’re using it as a force which is drawn from. You draw from chaos, and that is explained in Yennefer’s storyline especially, and it manifests in different ways. And you will see it as the audience how it manifests, and some familiar things which players of the game and readers of the books will understand.”
Cavill also confirmed that the reason his eyes were that way at the end of the trailer, was a result of taking a decoction, but when asked which decoction it was, Cavill said with a smirk, “I’m not going to reveal anything yet about that, because there are too many parallels drawn with other products as well, which we are not drawing parallels too.”
Source: IGN.com Henry Cavill Talks Magic in The Witcher and the Adaptation For Fans