To wit, it opened domestically on July 18, to the tune of $27.8 million, the highest opening weekend for a musical in U.S. history. Then it proceeded to stay in the top 10 at the box office through the weekend ending Sept. 7. For those keeping score, that's only two weeks short of when The Dark Knight dropped out of the domestic top 10; it went from No. 9 the weekend ending Sept. 21 to 13th for the weekend ending Sept. 28. The Dark Knight and Mamma Mia! opened on the same weekend, and everyone expected Mamma to get lost behind Knight. But the musical had legs of its own, and some unbelievable staying power.

Granted, The Dark Knight has made almost twice what Mamma Mia! has overall, with a total so far that's nearing $1 billion. But that's mostly thanks to domestic box office, and Mamma Mia! still has several foreign markets in which it's yet to open, including Japan. In other words, don't bet against Mamma to lead the global box office by the end of the year. Stranger things have happened.