Elise Graham takes part in the World Bog Snorkelling Championships 2017 with a rubber duck on her back on August 27, 2017 in Llanwrtyd Wells, Wales. The competition draws competitors from all over the world and is now in its 32nd year. (Photo by Matthew Horwood/Getty Images)

Ma Jiaqi, 5, and her mother arrive at Beijing Railway Station for their train to Changchun of Jilin province, in Beijing, China, January 25, 2016. According to traffic police, over 2.9 billion trips will be made around China during the 40-day Spring Festival travel rush, which started on January 24. (Photo by Jason Lee/Reuters)

Peruvian surfer Carlos “Huevito” Areola rides a reed board, or “caballito” (little horse), into a wave at Sydney's Bondi Beach, February 24, 2016. Areola is part of a group of Peruvian surfers touring Australia’s east coast to promote the use of the “caballito”. The “caballito” is thought to have been invented around 3,000 BC in northern Peru. (Photo by Jason Reed/Reuters)

A devotee is smeared with a vermillion powder while celebrating the “Sindoor Jatra” vermillion powder festival at Thimi, in Bhaktapur, Nepal, April 14, 2016. Devotees mark the festival by playing traditional drums, singing, dancing and carrying chariot of various deities around town while throwing vermillion powder to welcome the advent of spring and the New Year. (Photo by Navesh Chitrakar/Reuters)

A woman leans against one of the stones of the Stonehenge monument on the summer solstice near Amesbury, Britain on June 21, 2017. The annual festival attracts hundreds of people to the 5000 year old stone circle to mark the longest day in the northern hemisphere. sunrise was at 4.52am and was celebrated by dancing, music, and ritualistic events around the stones. (Photo by Neil Hall/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 jockey falls off during a traditional Barapan Kebo or buffalo races, in Taliwang, on the island of Sumbawa, West Nusa Tenggara, Indonesia November 22, 2015. Around 250 pairs of water buffalo took part in the Barapan Kebo ahead of the planting season, for prizes which included a top prize of a pilgrimage to Mecca. (Photo by Sigit Pamungkas/Reuters)

The interior of a house is damaged after an earthquake in Imphal, capital of the northeastern Indian state of Manipur, Monday, January 4, 2016. Five deaths have been reported from in and around Imphal due to falling debris. Imphal has a population of 270,000, and people were jolted from their sleep and ran out of their homes in panic. (Photo by Bullu Raj/AP Photo)