I immediately set about emailing shark experts. The Monterey Bay Aquarium declined to comment. The Vancouver Aquarium was more willing to put a toe in the water. "Honestly, I think the jury is still out on this question," emailed Ann Dreolini, a spokeswoman. "According to what I have read so far, there are people who believe the chance of a shark attack is greater while menstruating…and others who think this has absolutely no impact on shark attacks at all."
But Ralph S. Collier, a shark behavior expert who has been documenting shark attacks since 1963 and now heads up the nonprofit research and conservation group Shark Research Committee, told me about a study that his friend and fellow shark expert H. David Baldridge conducted in the late '60s. I couldn't find the study online, but according to Collier, Baldridge introduced several human body fluids—including menstrual blood—to captive wild sharks in open ocean pens to see if any would elicit a feeding frenzy. The only one that did cause such a reaction was peritoneal fluid, the liquid found in our abdominal cavity. (Unfortunately, said Collier, Baldridge's grant money ran out before he could figure out what was so bewitching to sharks about our gut fluid.)