A new interactive artwork has people staring into their shadows in Trafalgar Square, reports the BBC.

Under Scan, by the Canada-based multimedia artist Rafael Lozano-Hemmer, projects video portraits into the shadows of pedestrians with high-power projectors in front of London's National Portrait Gallery. The subjects of the video portraits appears to look directly at the viewer and interact, "then lose interest as the person walks away," according to the BBC.

"We actually count on people just walking by casting their shadow and all of a sudden you look down and go 'gee - there's somebody inside my shadow and they are waving at me,'" said Lozano-Hemmer, who also has an interactive work installed in New York's Madison Square Park through next Monday. Pulse Park, as that work is called, monitors visitors' pulse rates, then transmits them across the park in beams of light.

Under Scan will be on view in London through November 30.