A Mark IV tank, part of the parade at the Lord Mayor's Show in London. (Photo by Topical Press Agency/Getty Images). November 1917

Dog puppy “Sandy” protects against the rain with an umbrella fixed on her leash during a stroll in Rust, southern Germany, on May 26, 2013. (Photo by Patrick Seeger/AFP Photo)

A workman smooths out the gravel near the base of British artist Alex Chinneck' latest sculpture “A bullet from a shooting star” on the Greenwich Peninsula in London on September 17, 2015. The 35-metre tall, upside-down electricity pylon overlooks the Canary Wharf financial district. (Photo by Leon Neal/AFP Photo)

Storm chasing photographer Mike Hollingshead makes a living following the worst storms in America, from snarling tornadoes chewing up the Kansas farmland to supercell thunderstorms massing over the Dakotas. His style is to get right in the path of the storm. While he says it’s less scary than you think – because most of the storm consists of heavy rain – it’s still extremely stressful. Photo: Vivid sunset under severe storm in central Nebraska August 17, 2005. (Photo by Mike Hollingshead)

Passengers prepare to take part in the No Pants Subway Ride in Prague, Czech Republic, Sunday, January 8, 2017. The No Pants Subway Ride began in 2002 in New York as a stunt and has taken place in cities around the world since then. (Photo by Petr David Josek/AP Photo)

People walk down the street while Hurricane Matthew approaches in Port-au-Prince, Haiti October 3, 2016. (Photo by Carlos Garcia Rawlins/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.

The entire cast perform during a production media call for Singin' In The Rain at Her Majesty's Theatre on May 12, 2016 in Melbourne, Australia. (Photo by Robert Cianflone/Getty Images)