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Robots have become more humanoid over the years. Some look just like us and even have their own stylist, while others can compose music and even do blackflips. But the one telltale sign that a robot is, well, a robot is its stiff and rigid movements.

So scientists at the University of Colorado Boulder’s Keplinger Research Group created muscles for robots that allow them to be flexible like us. Their recent findings were published in the journals Science and Science Robotics.

They’re called HASEL actuators, which are strong enough to lift a gallon jug of water and nimble enough to pick up a tiny berry without crushing it. The artificial muscles are cheap to create; basically, they’re pouches (usually made from silicone or a material similar to a potato chip bag) filled with vegetable oil. Each bag is connected to electrodes that push the oil around, creating contractions and expansions like human muscles.

“We are just beginning to scratch the surface of applications,” researcher Timothy Morrissey told Quartz. ”We envision robots that look a lot like us rather than tin cans like R2-D2 or BB-9.” He imagines the technology can be applied to soft robots or used in prosthetics.

Watch our video above to see how the artificial muscles work.