A woman crosses an open sewer as she makes her way to her house in a Christian slum in Islamabad December 4, 2014. (Photo by Zohra Bensemra/Reuters)

Prayer flags fly at Namgyal Tsemo Monastery above the town of Leh in Ladakh, India September 24, 2016. High in the Indian Himalayas, young novice monks in maroon robes take their lessons inside the 15th-century Thiksey monastery. (Photo by Cathal McNaughton/Reuters)

In this December 13, 2014 photo, Ricardo Alegria holds his donkeys by a leash as he yells to sell their milk in the streets of Santiago, Chile. Alegria, along with his brother Marco, has been selling fresh donkey milk for the past 25 years, and says it's recommended as a vitamin boost. Shot glass size cups of the drink sell for about $2 dollars. Half a liter, which is the most he says his donkeys can give in one day, sells for about $20 dollars. (Photo by Luis Hidalgo/AP Photo)

Medics carry an injured at the explosion site in the busy center of Turkish capital, Ankara, Turkey, Sunday, March 13, 2016. The explosion is believed to have been caused by a car bomb that went off close to bus stops. News reports say the large explosion in the capital has caused several deaths and many casualties. (Photo by AP Photo)

Galagos, more commonly known as bush babies, are tiny African primates with remarkable jumping abilities. Thanks to the elastic energy stored in the tendons of their lower legs, small-eared galagos can jump 6 feet straight up in the air. (Photo by Traer Scott/Chronicle Books)

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.

Snow falls as a woman walks her dog in the village of Podolye, 70 kilometers (43 miles) east of St. Petersburg, Russia, early Thursday, May 11, 2017. North winds brought snow to the east of the St. Petersburg region. (Photo by Dmitri Lovetsky/AP Photo)

Snowfall views in Ercis district of Van, Turkiye on January 14, 2022. (Photo by Necmettin Karaca/Anadolu Agency via Getty Images)