The Knight's response to Roy's mockery was to simply make long, powerful strides towards the Alchemist officer; showing his naked aggression and telling his foe that there will be no more delays, no more distractions. The time has come for him to have his resolve and courage put to the test. Though what the Alchemist said about his weapon warranted a correction.

"Your pain and anger must be making you delirious, as my sword has never been alight with flame. You must be thinking of the Captain."

The Knight then looks towards a section of the battle line, only to visibly recoil in surprise when a massive nova of flames erupts from where the Knight-Captain presumably was, said fireball accompanied by the faint but distinctive cries and screams of people getting burned alive.

"...I did not expect that to happen..."

Knowing that such a destructive and indiscriminate technique being used means that his superior officer was cornered and desperate, the knight realizes that he has to finish this duel quick and come to the aid of his comrade before he inevitably exhausts his mana stores and is left at the mercy of his enemies. Making a quick step forward, the knight opens up with a diagonal cut aimed at hamstringing his sword-arm, if the officer was able to dodge or somehow parry the blow, the metal monster would deny his attempt to rally or retaliate by shoving into the Alchemist shoulder-first. Which considering how heavy that armor must seem despite the Knight's quickness, would probably be like getting rammed by a log.