In a giant warehouse in Reading, Massachusetts, I meet a pair of robots that look like goofy green footstools from the future. Their round eyes and satisfied grins are rendered with light emitting diodes. They sport small lidar sensors like tiny hats that scan nearby objects and people in 3D. Suddenly, one of them plays a chipper little tune, its mouth starts flashing, and its eyes morph into heart shapes. This means, I am told, that the robot is happy.

Stacks of vertical shelves weave around each other in what looks like an intricately choreographed – if admittedly inelegant – ballet that has been performed since 2014 in Amazon's cavernous warehouses. The shelves, each weighing more than 1,000 kg, are carried on the backs of robots that resemble giant versions of robotic vacuum cleaners. The robots cut down on time and human error, but they still have things to learn. Once an order is received, a robot goes to the shelf where the ordered item is stored. It picks up the shelf and takes it to an area where the item is removed and placed in a plastic bin, ready for packing and sending to the customer.