The creature says that " a circumstance that happened when I arrived on the confines of Switzerland...confirmed...the bitterness an horror of my feelings." what happened?

At length, a young girl comes running through the forest, and he hides himself beneath a cypress tree. As he watches, she suddenly stumbles and falls into the rapidly moving water; the creature, without thinking, leaps in and rescues her from certain death. As he is attempting to revive her, a peasant (presumably the girl's father) snatches the girl away from him, and shoots the creature when he attempts to follow. The creature bitterly contemplates this "reward for [his] benevolence," and is seized with a new, even greater hatred of humanity.