A soldier walks on the bank of the river in central Pyongyang, North Korea on April 16, 2017. (Photo by Damir Sagolj/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.

“Grit and Glamour”, a retrospective of the late British photographer Elsbeth Juda, who fled Nazi occupation and came to England in 1933, is at the Jewish Museum, in London, until July 1, 2018. Here: Shelagh Wilson, Copacabana beach, Rio de Janeiro, 1951. (Photo by Elsbeth Juda Archive/Victoria and Albert Museum)

Carla Bruni attends the L' Oreal Party at the Beach of The Palais du Festival during the 51st Cannes Film Festival on May 13,1998 in Cannes, France. (Photo by Foc Kan/WireImage)

People in Kathmandu joke that the face mask has now become part of the national dress – an indispensable accessory in an effort to protect themselves from the dust. Nepal has the worst air quality in the world, according to the Environmental Performance Index. (Photo by Pete Pattisson/The Guardian)

Activists from the People for the Ethical Treatment of Animals (PETA) demonstrate with slogans in protest of the designers use of fur, during the Paris Fashion Week, in front of the Eiffel Tower, in Paris, France, September 25, 2018. Placards read: “For a Fashion Week without fur”. (Photo by Benoit Tessier/Reuters)

A couple sit on the terrase of a cafe in Istanbul as seagulls fly over them on September 10, 2019. (Photo by Ozan Kose/AFP Photo)

A woman struggles to drink homemade alcohol poured from the mouth of an idol of “Swet Bhairab” during the annual Indra Jatra festival to worship Indra, Kumari and other deities and to mark the end of monsoon season in Kathmandu, Nepal on September 15, 2019. (Photo by Monika Deupala/Reuters)