[It's hard not to laugh at her astonishment. He won't go into the details of how exactly he knew, because it was all too obvious to him. It's not like these things are just something one inherently knows unless they've been trained or they fight a lot and have had to learn on their own.]

Of course! Using your own skeletal structure to your advantage will always be in your benefit. It's still going to hurt to punch someone, no matter what, but at least the chance of you really hurting yourself will go down quite a bit. Here.

[With her hand still in his, he moves her fist down so that the top of her hand lines up with her wrist.]

Punch like that, and it'll be much more solid. You'll have to practice to get used to positioning it like such, but once you get it, you'll be fighting with a much more advantageous technique. Why don't you punch me in my chest again? For real this time.