Jennifer Lopez Gets Loud for Hillary Clinton at Get Out The Vote concert on October 29, 2016 in Miami, Florida. (Photo by Larry Marano/Rex Features/Shutterstock)

Indian School children's in a traditational attire of a characters of Indian epic Ramayan, on the eve of children's day celebration at cubbon park, in Bangalore, India, 13 November 2016. Children's day (also known as Bal Divas), in India is celebrated every year on 14th of November to increase the awareness of people towards the rights, care, and education of children. Many schools hold activities and allow students to have fun and attend their classes in coloured dresses. (Photo by Jagadeesh N.V./EPA)

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.

Soldiers pose for a photo during the flower exhibition marking the 105th birth anniversary of the country's founding father, Kim Il Sung in Pyongyang, North Korea April 16, 2017. (Photo by Damir Sagolj/Reuters)

A woman walks through flood water during heavy downpour at a street in Genoa, Italy, 10 October 2014. At least one person died due to flooding after heavy rains caused the Bisagno river, which runs through Genoa city to overflow. Part of the city was in black-out with flooded streets and parked cars dragged away by the water's force. (Photo by Luca Zennaro/EPA)

A donkey savors warming temperatures after a long winter at the zoo in Warsaw, Poland, on Wednesday, April 8, 2015. (Photo by Czarek Sokolowski/AP Photo)

A Ukrainian man stands in protest in front of gunmen in unmarked uniforms as they stand guard in Balaklava, on the outskirts of Sevastopol, Ukraine, Saturday, March 1, 2014. (Photo by Andrew Lubimov/AP Photo)

During a jungle survival program February 20, 2013 taught by Royal Thai Special Forces in Sannapit, Thailand, U.S. Marines learned to catch cobras and drink their fresh blood, not to mention eat forest insects and pull the heads off of chicken. The training was part of Operation Cobra Gold 13, the 32nd edition of international military exercises hosted by the Thai. According to a U.S. Marines press release, Cobra Gold is the largest exercise of its kind in Asia and incorporates troops from five other nations in addition to the U.S. and Thailand. The Daily Mail reports that the Marines were invited to experience the local custom of drinking cobra blood after being taught to catch and kill cobras in the wild. As CNN notes, Cobra blood is believed to be a panacea and aphrodiasic in parts of Southeast Asia. In Jakarta, vendors can earn over $100 a night selling shots of cobra blood mixed with liquor. (Photo by Pornchai Kittiwongsakul/AFP Photo)