These Northern Lights “rainbows” have turned the sky greener than the Earth below. Vitaly Istomin, 26, spent several nights in freezing conditions under the stars in northern Russia’s Khibiny Mountains to capture the aurora’s “rainbows”. (Photo by Vitaly Istomin/Caters News Agency)

Fisherwomen laying barrels with salt in preparation for herring curing, 1937. (Photo by Topical Press Agency)

Hao Han (8), Shaolin kung fu student and child actor. Shaolin Monastery, Henan. (Photo by Mathias Braschler and Monika Fischer)

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.

As the sun sets on the Malecon in Havana on Friday January 23, 2015, Surenis Angulo de la Paz, 24, center, dances as group of locals play music around her. Behind her is Fidel Lopez, 55. (Photo by Sarah L. Voisin/The Washington Post)

A paper rhacophorus arvalis (farmland green tree frog) of Taiwan (R) is surrounded by paper pandas at an exhibition called “Pandas on Tour” at the National Theater in Taipei on February 24, 2014. Some 1,600 paper made pandas are on display, designed by French artist Paulo Grangeon. (Photo by Mandy Cheng/AFP Photo)

Children play with toy guns during Eid al-Fitr celebrations in Peshawar, Pakistan, 24 May 2020. Muslims around the world are celebrating Eid al-Fitr, the three day festival marking the end of the Muslim holy fasting month of Ramadan. Eid al-Fitr is one of the two major holidays in Islam. (Photo by Bilawal Arbab/EPA/EFE/Rex Features/Shutterstock)

A disabled child is buried up to his neck in sand during the partial solar eclipse in belief its rays can heal, in Karachi, Pakistan, 25 October 202. A partial solar eclipse occurs when a portion of the Earth is engulfed by the shadow (penumbra) cast by the Moon as it passes between our planet and the Sun in imperfect alignment. During this eclipse - the first of the decade – the Moon appears to cover the Sun, leaving the Sun's halo as a visible rim forming an annulus, popularly known as the 'ring of fire. (Photo by Shahzaib Akber/EPA/EFE/Rex Features/Shutterstock)