Jack winds up invalidating his answer a little simply by giving it.

"Which one do you want it to be?" It's a genuine question, and the implication is it's that one — which doesn't make for a very good foundation if it's threat. He's not even sure how he'd follow through. Bug her, maybe, but he doesn't... actually want to do that. First, because it sounds resoundingly uncomfortable and would draw too much attention to him. Second, because he's pretty sure she wouldn't tolerate it even if he tried, and he's not sure how exactly it is she'd retaliate. Some boys find that to be a challenge, they find it exciting, they pull pigtails. Jack has a long history and a cast on his arm that has taught him not to poke things knowing they come with consequences. He still has bruises on his ribs and his toes are too broken for him to really run. If she decided to stomp on his foot there's a very good chance he'd piss himself.

He figures if threat is the right answer it means he won't have to follow through, and if promise is the right answer, well, obviously he won't have to follow through either. He doesn't have to know which one is right if he lets her pick it herself.

If the answer is neither, well, he'll just go home. Maybe try again tomorrow, but earlier this time.