Waterproof books are the best invention since the rubber ducky. Directions for use: Sit behind her in the tub--her head resting on your chest. Read in her ear in a deep, low voice. Research suggests that women become more aroused through auditory stimulation than through visual. The stories may be cheesy, but hey, she's already wet. Aqua Erotica: 18 Stories for a Steamy Bath and Wet: More Aqua Erotica ($16, amazon.com)