When the first ability (the copy) resolves, you may choose to cast one of those cards. It's put on the stack, eventually resolves and goes to the graveyard, then the second instance of the ability resolves, allowing you to cast the other card. If you do, it goes on the stack as a spell, eventually resolves and goes to the graveyard. If you chose not to cast a card the first time around, you have two cards to choose from for this second instance.
What happens?
Former Rules Advisor
"Everything's better with pirates." - Lodge
(The Gamers: Dorkness Rising)
"Any sufficiently analyzed magic is indistinguishable from science."
(Girl Genius - Fairy Tale Theater Break - Cinderella, end of volume 8)