Angry Birds (video game) was being played, the staff liked the characters, and the team elected to design a game around them. In early 2009, physics games, such as "Crush the Castle", were popular flash-based web games, so the Rovio team was inspired by these games. During the development of "Angry Birds", the staff realized the birds needed an enemy. At the time, the "swine flu" epidemic was in the news, so the staff made the birds' enemies pigs. Angry Birds was the studio's 52nd produced game and on its initial release, the game did not sell many copies. After Angry Birds was a
Angry Birds (video game) hits of 2010". In December 2010, in honor of the one-year anniversary of the release of "Angry Birds", Rovio Mobile announced that the game had been downloaded 50 million times, with more than 12 million on iOS devices and 10 million on Android. By January 2014, the "Angry Birds" series had reached 2 billion downloads, including "Angry Birds", "Angry Birds Seasons", "Angry Birds Rio", "Angry Birds Space", "Angry Birds Star Wars I & II" and "Angry Birds Go!" On Christmas Day 2011 alone, 6.5 million copies of the various "Angry Birds" games were downloaded across all supported platforms. In the