Look at the image for long enough and you can make the train change direction simply by thinking about it. Freaky.

Just a week before Rio de Janeiro hosts South America's first Olympics, city residents expressed mixed feelings about the cost and security of the Games, while holding out hope they will bring joy to a nation facing economic and political crises. The conflicted thoughts mirror a recent survey by the Datafolha polling group showing that half of Brazilians were opposed to holding the Games, while 63 percent think the costs of hosting the event will outweigh benefits. (Photo by Pilar Olivares/Reuters)

Everyone wants to get something for nothing - whether it's a lucky upgrade that means you can turn left when you get on a plane instead or heading off into the economy seats, or even getting a few extra features thrown in for free when you buy a new car.

As some of the sharpest businesses around, no-one understands this quite as well as casinos and that's why they all have a system that they call comps. It's short for "complimentary offers" and these are special treats specially designed to reward you for your loyalty to the casino in question. They're basically bonuses.

Russian soldiers write home while serving on the Eastern Front during World War I, circa 1915. (Photo by Hulton Archive/Getty Images)

Kylie Jenner attends the 2019 Met Gala celebrating “Camp: Notes on Fashion” at the Metropolitan Museum of Art on May 06, 2019 in New York City. (Photo by Andrew Kelly/Reuters)

US-British actress Lily Collins arrives for the 2023 Met Gala at the Metropolitan Museum of Art on May 1, 2023, in New York. (Photo by Angela Weiss/AFP Photo)

British Liberal politician Cyril Smith relaxes on the beach at Margate, prior to the morning session of the annual Party Conference. (Photo by Keystone/Getty Images). 1979

A frightened maid, played by Phoebe Hodgson, knocks a bust off a tall pedestal while dusting, in a scene from the play “Queen High” at the Queen's Theatre. (Photo by Sasha/Getty Images). 1926