The painted nails of a Kurdish Peshmerga female fighter are seen as she takes up a position during combat skills training before being deployed to fight Islamic State militants, at their military camp in Sulaimaniya, northern Iraq September 18, 2014. (Photo by Ahmed Jadallah/Reuters)

A man rides a horse through flames during the annual “Luminarias” celebration on the eve of Saint Anthony's day, Spain's patron saint of animals, in the village of San Bartolome de Pinares, northwest of Madrid, Spain, January 16, 2017. (Photo by Paul Hanna/Reuters)

DJ David Guetta (R) and rapper Nicki Minaj perform onstage during the 2017 Billboard Music Awards at T-Mobile Arena on May 21, 2017 in Las Vegas, Nevada. (Photo by Mario Anzuoni/Reuters)

Princess Charlene poses after the arrival of the Riviera Water Bike Challenge in support of the Princess Charlene of Monaco Foundation, in Nice, France, June 4, 2017. (Photo by Eric Gaillard/Reuters)

A tamed hawk attacks a rabbit during the traditional hunting contest outside the village of Nura, east from Almaty, Kazakhstan, February 13, 2016. (Photo by Shamil Zhumatov/Reuters)

Zamora, 55, self-employed, poses for a photograph in front of the Cuban and U.S. flags after buying a pineapple in Havana, March 25, 2016. Regarding Obama's historic visit to the island, Zamora said “It's good for the Cubans that he came and re-established relationships between the two countries”. (Photo by Ueslei Marcelino/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.

A reveller performs while attending the block party “Galo da Madrugada” during carnival festivities in Sao Paulo, Brazil on February 25, 2020. (Photo by Rahel Patrasso/Reuters)