The Spec has a light, but interesting and possibly useful story about the aphrodisiac qualities of watermelon.

I always eat loads of watermelon. I had no idea.

How does this magic work? Well, watermelons contain citrulline in the flesh and rind. It reacts with the body’s enzymes when consumed in large quantities and is changed into arginine.

“Arginine boosts nitric oxide, which relaxes blood vessels, the same basic effect that [a certain drug] has to treat erectile dysfunction and maybe even prevent it,” said Bhimu Patil, a researcher and director of Texas A&M’s Fruit and Vegetable Improvement Center.
— Watermelon may juice up your sex life, scientists say Hamilton Spectator 4 Jul 2008

Here is the wire story on which the Spec story is based.

• Watermelon yields [erectile function drug]-like effects, scientists say TheRecord.com 2 Jul 2008