The animal instinct is familiar to Robb, something that has since shaped him since returning to life. Lauralae didn't seem threatening, the animal side of him normally able to sense if something wasn't completely right (though that was never a guarantee). He made the difficult decision to extend a measure of trust to her, willing to teach her combat.

It could blow up in his face, but it wasn't the first mistake he fell into

"It is, it has more weight to it too. If you don't hold it a certain way, I could give you a tap and the sword will fall from your hands." He bumped his sparring sword against hers, not hard enough to actually knock it out of her grip, but to emphasize the point.

He hesitated but moved next to her, adjusting her hand so that she could properly hold the sword. "This is the stance," he fell into the pose to show her, ready to help her shift her body if she allowed it.