A visitor looks at a monumental sculpture by artist Robert Therrien in the newly opened Metropolitan Arts Centre in Belfast, Northern Ireland, in this April 23, 2012 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Cathal McNaughton/Files)

A security guard jokingly inspects the back of a self-portrait entitled “Mask II” by Australian sculptor Ron Mueck at the Royal Scottish Academy in Edinburgh, Scotland, in this July 31, 2006 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/David Moir/Files)

A man jumps into the cool water of the Dnipro river in Kiev, Ukraine, in this June 11, 2010 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Konstantin Chernichkin/Files)

A man controls a ball during his soccer practice in a public park on a foggy morning in Agartala, capital of India’s northeastern state of Tripura, in this January 12, 2015 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Jayanta Dey/Files)

Shoppers are seen at a soon-to-be-opened shopping centre in Singapore’s Orchard Road district in this January 11, 2009 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Vivek Prakash/Files)

Philadelphia Phillies Ben Francisco reacts after being hit in the head with a pitch by Cincinnati Reds Logan Ondrusek during the MLB National League Division Series baseball playoffs in Philadelphia, Pennsylvania, United States in this October 8, 2010 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Tim Shaffer/Files)

The rear end and head and shoulders of Eurasier dogs Tinu (L) and Uno (R) are seen from behind a tree in Green Park, central London, Britain, in this February 24, 2004 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Natasha-Marie Brown/Files)

Nissan Motor Co vehicles are parked at the company’s factory in Yokosuka, south of Tokyo, Japan, in this November 4, 2009 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Toru Hanai/Files)

Jonathan Aubrey, 25, a visitor from Britain, stands in between “Mirrors of Invisibility” as part of a series of mirrors demonstrating various types of reflection at the Hong Kong Science Museum, in this October 6, 2009 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Bobby Yip/Files)

People swim at the sea in Havana, Cuba, in this April 28, 2015 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Alexandre Meneghini/Files)

Liu Bolin, a Chinese artist, blends himself into the background in front of a shelf lined with comic books as part of a series of performances in Caracas, Venezuela, in this November 2, 2013 file photo. When seeing is not believing – the wonderful world of optical illusions. Eleven pictures from the archive that will make you doubt your eyes. (Reuters Photo/Jorge Silva/Files)