Sometimes the best twist is not a surprise. Jeffrey Eugenides could have concealed the nature of Cal Stephanides' condition, could have saved it for a big reveal and dropped only tantalizing hints throughout the narrative. Instead, he announces that Cal is an intersex man upfront, and then proceeds to tease us for the rest of the story. Eugenides makes the reader into a participant in Cal's indulgent memoir instead of an audience; we're in on…