There's a simple four-letter word for the impossibly complex combination of psychology and physiology that gets hearts racing, palms sweating, faces blushing, and more when two people are attracted to one another. Not love. Lust. It can be pretty difficult, if not impossible, to tell the two apart. In Delirium, Lena sure doesn't know the difference. In fact, the word "lust" isn't even used in the book. But the way Alex gets her motor revving before she even knows his last name tells us that it's not simply love that's driving everyone crazy: it's lust, too.