Gunfire erupted at a Denver pot celebration Saturday, injuring two people and scattering a crowd of thousands who had gathered for the first 4/20 counterculture holiday since the state legalized marijuana... Photo: A woman smokes a large marijuana joint at the Vancouver Art Gallery during the annual 4/20 day, which promotes the use of marijuana, in Vancouver, British Columbia April 20, 2013. (Photo by Ben Nelms/Reuters)

Zookeepers measure the length of a pueblan milk snake in the Reptile House of ZSL London Zoo as part of their annual weighing and measuring of their animals on August 25, 2011 in London, England. The heights and weights of over 750 different animal species at the zoo are recorded into the International Species Information System, to monitor their health and share the data with other zoos across the world. (Photo by Oli Scarff/Getty Images)

Steampunk enthusiasts attend the sixth annual Haworth Steampunk Weekend in Haworth, northern England on November 25, 2018. The three-day alternative lifestyle festival features: music, dancers, entertainers, burlesque performers, vintage vehicles, a fashion show and a masquerade ball. Steampunk is a subgenre of science fiction or science fantasy that incorporates technology and aesthetic designs inspired by 19th-century industrial steam-powered machinery. (Photo by Oli Scarff/AFP Photo)

Festive characters perform during Harrods 26th Annual Christmas Parade on November 5, in London, England. (Photo by Steve Finn/Harrods via Getty Images)

A Sumatran Tiger looks at visiting children from it's enclosure during the ZSL London Zoo's annual stocktake of animals on January 5, 2015 in London, England. The zoo's annual stocktake requires keepers to check on the numbers of every one of the 800 different animal species, including every invertebrate, bird, fish, mammal, reptile, and amphibian. (Photo by Dan Kitwood/Getty Images)

A half-naked shrine parishioner using a wooden tub pours cold water onto himself during an annual cold-endurance festival at the Kanda Myojin Shinto shrine in Tokyo, Saturday, January 10, 2015. Pouring cold water on their bodies is believed to purify their souls. (Photo by Eugene Hoshiko/AP Photo)

Participants wearing costumes take part in the West Indian Day Parade in the Brooklyn borough of New York September 1, 2014. The parade, which draws a crowd of a million plus, celebrates Caribbean culture. (Photo by Eric Thayer/Reuters)

Chincoteague Ponies swim across Assateague Channel in a heavy downpour on Wednesday, July 24, 2013 during the 88th Annual Chincoteague Pony Swim. A portion of the herd will be auctioned on Thursday. (Photo by Jay Diem/Eastern Shore News)