When he was four years old, Herbert was witness to a frightening event when he was at the local park in the company of the family's maid. A cart horse pulling a heavy load collapsed. Herbert became fearful of going out into the street, with his fear focused on horses and heavily loaded vehicles, which he was afraid would fall over. This fear was interpreted as a neurosis (equinophobia). Herbert's father initially attributes the neurosis to "sexual over-excitement caused by his mother's caresses" and fear caused by the large penises of horses. While not rejecting these explanations, Freud gradually encourages the father also to understand Herbert's disorder in terms of the anxiety caused by the arrival of his younger sister and an inadequately satisfied curiosity as to the origin of babies. Although a number of sexual and excretal fantasies and anxieties (such as Oedipal wishes and castration anxiety) are explored during the case history, Freud does not ultimately explain the case in terms of these factors, and on occasion reproaches Herbert's father for sticking too dogmatically to a rigidly Oedipal understanding of his son's anxiety. Freud also regrets the parents' unwillingness to tell Herbert the truth about coition.