The next surprise, captured by several high-speed videocameras, was that instead of digging in for extra purchase, the snakes flattened themselves more smoothly against the sand, every time the researchers tilted the "dune" more steeply.
Furthermore, it was only sidewinding rattlesnakes - a species called Crotalus cerastes - that used this strategy. Thirteen related species of pit viper, faced with the same challenge, tried other wriggling techniques and got nowhere, with the exception of one: a speckled rattlesnake that inched its way very slowly up the incline using a concertina motion.
Sidewinders, on the other hand, Dr Goldman said, "could basically ascend any sand dune we threw at them".
To test out their findings in detail, Dr Goldman's team of physicists and biologists contacted robotics engineers at Carnegie Mellon University in Pittsburgh.
There, Prof Howie Choset and his lab, external had been working on sidewinding robots for several years. Their designs are aimed at various applications, from search-and-rescue to surgery.
But Prof Choset's robotic sidewinders were troubled by the very same challenge that the snakes had a knack for: sandy ascents.
Adjusting Elizabeth's settings also allowed the collaboration to figure out other secrets to the sidewinders' success.
In particular, their motion boils down to a surprisingly simple combination of a horizontal and a vertical wave: a left-right slither, along with up-and-down movement, both travelling down the body but slightly out of sync.
"If you phase those waves just right, you get sidewinding," Dr Goldman explained.
Flattening or enlarging the vertical wave allowed Elizabeth to get just the right amount of contact with the sand. Too much, and the robot would slip; too little, and it risked tipping over.
The reason all these adjustments help the snakes and robots to climb is because they keep the sand more stable underneath them. Getting enough purchase without making too much sand flow downhill is a delicate balancing act.
"What we noticed was that when the snake's ascending effectively... the material behind it was in a nice solid state. And when we applied the changes to the robot, we found a similar feature of the interaction, such that the material didn't flow much," said Dr Goldman.