The researchers developed a theory: Perhaps the sudden, high-frequency rattle of the snakes created an illusion of closeness that acts as a warning. Dr. Chagnaud wanted to test this theory on buffalo at the Munich Zoo first before realizing it would be much easier to use college students, who are usually more willing subjects.
The volunteers sat in a chair in the middle of a room and wore a virtual reality headset that moved them through a grassland to a hidden snake at dusk. As the rattle became more common, the volunteers pressed a button to indicate when they believed they were about three feet from the line. All test subjects pressed the button as the rattle jumped in frequency, misinterpreting their actual distance.
The researchers suspect that this sudden jump in frequency is an evolved behavior that rattlesnakes use to deceive listeners about their actual distance from the snake. “The shift in the rattle is an illusion of the snake,” said Bruce Young, an anatomist at Kirksville College of Osteopathic Medicine, Missouri, who reviewed the work.
Mentioning this pretext is only a hypothesis, stated Dr. Chagnaud, of course. In another explanation, the quick rattle could be a strategy to get the listener’s attention, similar to creating a terrifying reaction, such as when a loud noise makes a person twitch. But dr. Chagnaud points out that a snake could more efficiently generate a startle response by jumping from 3 Hertz to 100 Hertz; He believes the slow, rattling ramp-up to 100 Hertz is better explained by an illusion of closeness.
But humans were never a rattlesnake’s intended evolutionary target, as the snakes have lived in North America for at least six million years. Dr. Rowe said the paper doesn’t necessarily shed light on how the animals that evolved with the rattlesnakes, such as badgers or canids, perceive the rattle.
Unfortunately, doing the same virtual reality experiment on a Mustelid would likely be chaotic and stressful. “Could you put little protective goggles on a badger?” Wondered Dr. Rowe loudly. “Badgers are so persistent.” In his eyes, California ground squirrels would be a rattlesnake enemy that is much better suited to virtual reality.
“There are a lot of bright young scientists out there who might find a way to put a squirrel with little headphones on to a monitor,” said Dr. Rowe.