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) the top 10 for paid iPhone/iPod apps, while its iPad-exclusive "Angry Birds HD" versions were the top-selling and top-downloaded iPad apps for the year. Mattel also made a few board games based on the app. These were called "Angry Birds: Knock on Wood, Angry Birds: On Thin Ice" and "Angry Birds: Mega Smash". In February 2010, "Angry Birds" was a nominee for the "Best Casual Game" award at the 6th annual International Mobile Gaming Awards in Barcelona, Spain. In September 2010, IGN named "Angry Birds" as the fourth best iPhone game of all time. In April 2011, "Angry Birds" won