A rooster bred for its all black appearance walks through the yard of a small backyard farm on February 3, 2017 on the outskirts of Jakarta, Indonesia. The roosters, called Ayam Cemani, are completely black including their bones and meat and are often sold for use in rituals. (Photo by Ed Wray/Getty Images)

A boy moves away as a United Nations World Food Programme (WFP) helicopter lands in Rubkuai village, Unity State, northern South Sudan, February 18, 2017. South Sudan on Monday declared famine in some parts of the country, with more than three years of war leaving nearly five million hungry in what aid groups called a “man-made” tragedy. (Photo by Siegfried Modola/Reuters)

A woman lies injured after an incident on Westminster Bridge in London on Wednesday, March 22, 2017. A police officer has been stabbed near to the British Parliament and the alleged assailant shot by armed police. Scotland Yard report they have been called to an incident on Westminster Bridge where several people have been injured by a car. (Photo by Toby Melville/Reuters)

Somalis remove the body of a man killed in a blast in the capital Mogadishu, Somalia Saturday, October 14, 2017. A huge explosion from a truck bomb has killed at least 20 people in Somalia's capital, police said Saturday, as shaken residents called it the most powerful blast they'd heard in years. (Photo by Farah Abdi Warsameh/AP Photo)

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.

This picture taken on October 18, 2018 shows a “trolley boy” pushing a home- made cart along a train track in Manila, Philippines. Scores of commuters in the city of about 12 million are propelled to their destinations daily by so-called “trolley boys” pushing metal carts that ply a few segments of the sprawling capital's railroads. (Photo by Noel Celis/AFP Photo)

Members of the Castellers “Vila de Gracia” start forming their famous human tower called “castell” in the Barcelona neighborhood of Gracia, Catalonia, Spain on Sunday May 19 2013. A “castell” is a human tower traditionally built during festivals in many places in Catalonia. At these festivals, several "colles" or teams compete to build the most impressive towers they can. (Photo by Emilio Morenatti/Associated Press)