Jacob had deliberately mentioned the forest because he wanted to see Matilda’s blushing face.
Even if she was a very calm and composed person, she would still be embarrassed when she recalled their presumptuous youth and the sweet and ambiguous past that the both of them shared.
Jacob felt that he would have to make Matilda think more about the past. If he constantly reminded her of the past that made her heart feel a little turbulent, then he would definitely be able to evoke the fire in her