"I never said you had to be confrontational or aggressive Grace, water is a force, but not with ill will.  Even streams can carry away a tennis ball," he smirked a little, it was meant to calm her down, but he may have only agitated her more.

"look why don't we start off with something simple," as tempted to see how much force with water she could produce, he didn't want to give her a heart attack by forcing her to do something so 'aggressive', Instead he picked up a tennis ball that had landed close nearby during their exercise. "Ok, so this thing isn't going to be coming at you at 60 mph, instead, I want you to just show me what you can do with it, and by that, I mean how well you can manipulate this physical object with water."