Swoosh. Boom. A big white bird clocks a young girl and knocks her off balance. The swan beats its wings ferociously as it lands on top of her. He caresses her thighs with his webbed feat and holds the back of her neck in his bill. She can't escape as the swan presses down with his chest on her own.
The bird opens the girl's thighs, and her hands are too frightened and confused to resist. The fast-moving bird on top of her looks like a blur of white feathers, and she can feel his heart beating.
The swan completes the act, and Leda becomes pregnant. She will give birth to Helen of Troy, the woman over whom the Trojan War will be fought. In Ancient Greek mythology – and in Yeats's poem – Leda's rape is taken as an indirect a cause of war.
The speaker wonders if Leda acquired any of Zeus's knowledge as the swan overpowered her. Did she know she was having sex with a god? She didn't have too long to think about it, because as soon as the swan had gotten what he wanted, he let her fall to the ground as if he couldn't care less.