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) history of the Apple App Store, "Angry Birds" holds the record for most days at the top of the Paid Apps chart, having spent a total of 275 days at the No.1 position; "Angry Birds Rio" has been No.1 for a total of 23 days, ranking ninth on the list. In Apple's "iTunes Rewind" list of the most popular iTunes Store media for 2011, "Angry Birds" was the top-selling paid iPhone/iPod app on the App Store and its free version was the fourth-most downloaded. The game's two special-edition versions, "Angry Birds Seasons" and "Angry Birds Rio", were also ranked in