Why just want to grab hold of Curleys wife's hair and not let go?

Curley's wife observes that Lennie is "jus' like a big baby" (99) and invites him to stroke her soft hair. Lennie begins to feel her hair and likes it very much indeed, which leads him to pet it too hard. Curley's wife begins to struggle, which sends Lennie into a panic. He grabs a hold of her hair and muffles her screams. When she continues to struggle, Lennie grows angry. He shakes her violently, telling her to keep quiet so that George doesn't hear her. Before he knows it, he has broken her neck.