By Not since the invention of bacon and eggs has the collision of fowl and swine tasted so good.

A game called Angry Birds is dominating the best-selling-applications charts for Apple's iPhone with a simple, whimsical premise: Players turn different species of scowling birds into projectiles with which to crush a collection of grunting pigs scattered around various ramshackle structures. More than 12 million copies of Angry Birds have been sold since it went on sale late last year, most of them 99-cent downloads for iPhones and iPod touches, according to Rovio Mobile Ltd., the Finnish company that created the game.

Why do smart people love seemingly mindless games? Angry Birds is one of the latest to join the pantheon of 'casual games' that have appealed to a mass audience with a blend of addictive game play, memorable design and deft marketing. The games are designed to be played in short bursts, sometimes called 'entertainment snacking' by industry executives, and there is no stigma attached to adults pulling out their mobile phones and playing in most places. Games like Angry Birds incorporate cute, warm graphics, amusing sound effects and a rewardsystem to make players feel good. A scientific study from 2008 found that casual games provide a 'cognitive distraction' that could significantly improve players' moods and stress levels.

Casual games are defined by the ease with which they can be picked up, including by players bewildered by more complex 'hardcore games' for PCs and consoles, with their intricate story lines and controls. The category spans early sensations like Tetris, the Russian-made puzzle game for PCs and consoles from the 1980s, to Bejeweled, a decade-old shape-matching game that is still in wide use in mobile devices. The average mobile-game player is 45 years old and nearly as likely to be female as male, according to a survey last year of more than 1,100 customers of AT&T's wireless service sponsored by PopCap Games, the maker of Bejeweled and other titles. When asked where they play mobile games, the top answer from respondents to the survey, conducted by Information Solutions Group, was while waiting for an appointment.

Angry Birds has attracted an unusually high-brow roster of fans. U.K. Prime Minister David Cameron has said he plays the game on his iPad, according to Andy Payne, chairman of a British games-industry trade group, who spoke to Mr. Cameron at a group dinner in September. (A spokeswoman for the prime minister didn't return a request for comment.) The author Salman Rushdie in a recent radio interview called himself 'something of a master at Angry Birds.' And comedian Conan O'Brien posted a YouTube video recently to promote his new talk show, in which he boasts that he's on level four of Angry Birds.

Mikael Hed, chief executive of Angry Birds-developer Rovio, says the game's success is 'really the sum of all of its parts,' including the edgy-but-cute characters, amusing sound effects and simple rules. Rovio started in early 2009 with a rough idea of the protagonists it wanted to feature -- a cast of stern-looking birds. It decided to make the game's villains a group of sickly-looking green pigs, in homage to the swine-flu pandemic then grabbing headlines. The reason the birds are so angry with the pigs, according to the back story of the game, is that the pigs swiped the birds' eggs to cook them up.

Rovio spent about $100,000 on the original Angry Birds and has invested more in new game levels that it offers, free, through updates to the game, a Rovio spokesman says.

Fueled by word of mouth, the game landed on the best-seller chart for Apple's App Store for Finland late last year. In February, when Apple made Angry Birds a staff pick in the U.K. App Store, sales exploded, Mr. Hed says. A couple of months later, the game became a best-selling paid app in the U.S. App Store, he says.

Nick Wingfield