The Witcher may not arrive on Netflix until December 20th, but star Henry Cavill is getting ahead of the curve by explaining just what exactly a Witcher is in this new video. Granted, it's a little spoilery since it reveals quite a few moments from the early episodes of the series, but if you really want to know what a Witcher is all about before watching the show, this is an excellent primer. And all the better for explaining what makes Geralt of Rivia tick. Cavill and the creative team are coming out in force in support of the …