Lex is more than proficient with swords, guns, and hand to hand combat, but knives are a huge blind spot in his training from back home. He couldn't back down now after seeking this woman's help and decided to use what he did know and apply it to the blade.

Taking the handle he has no trouble opening the switchblade and not a moment later lunges at Sonja with it, knife directed at her neck. His manner of movement most likely gives away that he is primarily a swordsman, but what he lacks in technique he makes up for in audacity.