Rummaging in a bin for scraps, this fox in Barnet, north London, England found itself trapped in the lid on May 23, 2019. Luckily the Royal Society for the Prevention of Cruelty to Animals were able to free it. (Photo by RSPCA/PA Wire Press Association)

Ana Ivanovic of Serbia plays a backhand return to Maria Sharapova of Russia during their women's singles final match at the Brisbane International tennis tournament in Brisbane, January 10, 2015. (Photo by Jason Reed/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.

Battersea Power Station. The chimney rims are thinner on top than you might expect. (Photo by Bradley L. Garrett)

A Ukrainian serviceman of the 65th mechanized brigade smoke on position of a Soviet-made 2s1 Gvozdyka 120mm howitzer in the Zaporizhia region, Ukraine, 15 November 2023, amid the Russian invasion. Russian troops entered Ukrainian territory in February 2022, starting a conflict that has provoked destruction and a humanitarian crisis. (Photo by Kateryna Klochko/EPA)

Sorana Cirstea of Romania hits the ball against Jie Zheng if China during the Sony Ericsson Open at Crandon Park Tennis Center on March 22, 2011 in Key Biscayne, Florida.

Bus 392 stands on the highway running from Beersheva to Eilat, with windows broken following a gun attack on August 18, 2011 near the Israel - Egypt border, Israel. A series of coordinated gun and roadside bomb attacks against miltary and civilian targets near the Israeli - Egyptian border, including an ambush on the bus travellling 20km north of Eilat, are reported to have left 5 dead and many injured. (Photo by Yehuada Ben Itah/Getty Images)

People try to board a goverment bus during the second day of a suspension of public transport services in Apopa, El Salvador July 28, 2015. Violent gangs in El Salvador ordered bus drivers to strike on Monday in a conflict that has killed six people and left thousands of commuters stranded on the streets of the Central American capital, police and bus company officials said. (Photo by Jose Cabezas/Reuters)