"What's This?" describes the moment just before Leda's violation. It is a response to Ragain's opening lines:
" I lie in the wreckage of my longing
which called him down to me.
I remember myself before Zeus settled
over me,..... That world is gone."
As a prequel my point is to create ambiguity. What longing? Why the piglet and nest? What does her expression reveal to you?