In Terminator 2: Judgement Day, the heroes flee from the T-1000 terminator, a liquid metal murder-bot, in a psychiatric prison.
As the T-1000 pursues them down a hall, it's seemingly stopped by barred gates. Except the terminator melts straight through the bars, barely losing a step.
Go figure.
Scientists at China's Sun Yat-Sen University have actually made a small robot that, like the T-1000, can turn to liquid and then reform back as a solid. They even recreated the eerie through-the-bars scene, jailbreaking a Lego-shaped bot from a barred cell.
How? Scientists created a Lego figurine made of liquid metal. Then, using magnets, they melted the figurine down, allowing the tiny robot to slip through a set of bars. This was achieved by using a metal called gallium, which has a melting temperature of just 86 degrees F. They then embedded magnetic metals within the liquid metal, allowing them to heat up the gallium with magnetic fields, turning it to liquid. After that, the liquid was moved using magnets and the original Lego-shaped robot was reformed. Scientists have labelled the bot a magnetoactive solid-liquid phase transitional machine.
Mind you, the current liquid robot is far from a sentient killing machine.
Scientists think this may have more benign uses, such as using the liquids to encapsulate objects, say a sharp piece of metal, in the body. Once encapsulated, the objects can be more safely evacuated from the body.
Interesting enough, the biggest inspiration for the liquid robot was not science fiction, but instead science-fact. Real-life sea cucumbers can alter their own rigidity to reduce physical damage and increase their weight-bearing capabilities. Meanwhile, octopuses aren't quite liquid, but can change their rigidity to squeeze through tight spaces, among other things.