If we were to burn NH4Cr2O7 with HgSCN in the Dark Ages in Europe and show it to anyone, it is us who would be burning next on a fiery cross of Inquisition. And it’s no wonder, since this experiment produces a truly marvelous result. At first, as you ignite the mixture of NH4Cr2O7 and HgSCN, all you can see is that it is slowly burning with a reddish flame. After a while, however, a crater is formed in the middle of the burning pile, and then, suddenly, tentacle-like appendages start sprouting from the burning mixture. And you can almost hear the scream of the mad occultist – “Come forth, Kraken! Come forth!” But of course, this is simply a chemical reaction that is called the "Pharoah's Serpent". It was also often sold in firework stores until people realized that it was toxic.

In Dougie Wallace’s photos of Mumbai taxis, the chatter, yelling, and constant horns of the city are almost audible. A selection of his images is on show at Gayfield Creative Spaces, Edinburgh, as part of the Retina photography festival until 30 July. For four years, the Glasgow-born Wallace focused his photos on one kind of taxi in particular: the Premier Padmini, a 1960s workhorse painted in black and yellow. Locally known as “Kaali-Peeli”, there were once more than 60,000 of them in the Indian city. But thanks to laws restricting pollution, the cars now are fast disappearing from Mumbai’s streets. (Photo by Dougie Wallace/The Guardian)

Hot Tub Cinema is an experience like no other. Combining relaxing hot tubs, great films and amazing spaces, it is a luxurious event that celebrates film in a fun and engaging way. Attendees can purchase whole tubs to share with friends or buy individual tickets to share with fellow hot tubbers. The tubs are cleaned, refilled and heated before every show. Popping-up throughout the year in London and around the UK, Hot Tub Cinema is also preparing to tour internationally in the near future. During the summer, we takeover rooftops in central London with astounding views across the city's inimitable skyline. For the autumn/winter we move indoors to continue the fun hidden away from the unpredictable weather.

An image produced by the Hubble telescope of the perfectly “edge-on” galaxy, or NGC 4013, March 1, 2001. This new Hubble picture reveals, with great detail, huge clouds of dust and gas extending along, as well as far above, the galaxy's main disk. NGC 4013 is a spiral galaxy, similar to the Milky Way, lying some 55 million light-years from Earth in the direction of the constellation Ursa Major. Viewed face-on, it would look like a nearly circular pinwheel, but NGC 4013 happens to be seen edge-on from our vantage point. Even at 55 million light-years, the galaxy is larger than Hubble's field of view, and the image shows only a little more than half of the object, albeit with unprecedented detail. (Photo Courtesy of NASA/Newsmakers)

Having $100 in your pocket would be so much cooler if it was designed by Martin Joubert. He went all out and created a number of different designs for the 100 USD banknotes, ranging from silly to witty. We especially liked the one with “That’s right. This is real money” written on it, showing just how many cups of coffee, basketballs, and guns you can buy with 100 dollars. All in all, even the currency that we have today is nothing but paper, even though it looks official and strict. There is nothing backing it up except for our noble military that ensures that Gulf States sell their oil using only the “green” kind of currency. (Photo by Martin Joubert)

In this picture taken on June 24, 2017 participants take part in the “Women's Beautiful Buttock series” contest shopping mall in Shenyang, Liaoning province. Ladies from different parts of China gathered in Shenyang to show off their perfect curves during the competition. While it is unclear who ended up taking home 1st place, it looks like everyone had a good time regardless of whether or not they won the title. In November 2016, Brazil held a similar competition, Miss BumBum, which was attended by more than 10 million people. Erika Canela, a 24-year-old beauty from Bahia won the main title of the contest. (Photo by AFP Photo/Stringer)