Some moviegoers were doing it anyway, but the other spectators who find it hard not to dance and sing along to "Dancing Queen" will be very pleased to find out that Universal Pictures plans to boost its Labor Day weekend earnings for its movie musical "Mamma Mia!" by releasing "Mamma Mia! The Sing-Along Edition."

Universal Pictures’ movie is already a hit as it cashed in approximately $320 million worldwide and about $117 million in the United States. As of last weekend, it was just $2 million shy of beating "Hairspray" ($119 million) to become one of the best-earning musicals of all time and enter a select company: "Grease," "Chicago" and "The Sound of Music."

The new version of “Mamma Mia!” will include subtitled lyrics to all the tunes from "Dancing Queen" to "Waterloo" so enthusiastic viewers can sing along the classic ABBA hits. More details about "Mamma Mia! The Sing-Along Edition" will soon be available on the movie’s official Web site. The Sing-Along Edition opens in limited release on August 29.

The adaptation after the West End stage musical - produced by Universal Pictures in collaboration with Playtone and Littlestar - already had the most successful opening weekend of any musical movie in U.S. history.

For those of you who still don’t know, the ever-wonderful Meryl Streep plays the film’s main character (single mother Donna Sheridan), while Pierce Brosnan, Colin Firth and Stellan Skarsgård have the roles of the three men who fight for Donna’s heart and for the privilege to become a father for the singer’s daughter Sophia (Amanda Seyfried).