In fact, what makes the Hulk so dangerous to his completely male antagonists is that he combines the stereotypes of masculinity (strength, aggressiveness) with the frightening out-of-control emotional tsunamic force typically associated with women. Perhaps why Betty Ross can calm the beast is because he represents a force of liberation that will take her away from the suffocating influence of her father. She can identify with the Hulk's ability to smash through social constraints, and the forces which chain the personality, because she also feels these restrictions. When Betty asks Bruce what it feels like to become the Hulk he mentions three keywords: "Strength, power, and freedom." Mighty tempting to people who are encroached on all sides by forces of male authority. Bruce also has to fend off slimy Glenn Talbot (Josh Lucas), a competitor for Betty's favours, and a man who aligns himself with the representation of patriarchal dominance (aka the Military).

The film culminates in the classic Freudian showdown between father and son, which results in Bruce's eventual freedom from his father's overshadowing legacy. He is now capable of establishing his own independence. Alas, no such luck for Betty. Without the Hulk she returns to being constrained and spied upon her by father. It's such a classic reading of the film that I assume that Ang Lee is chuckling somewhere about it.