Erotic thriller Fifty Shades Of Grey has continued to titillate movie fans by adding another $23.2 million (£14.5 million) to its haul to retain the North American box office crown.

The film adaptation of E. L. James' raunchy books, which stars Jamie Dornan as bondage-obsessed businessman Christian Grey, manages to maintain a stranglehold on the top of the charts, again beating Colin Firth's Kingsman: The Secret Service, which scores a $17.5 million (£10.9 million) take in its second weekend (20-22Feb15) on release.

The Spongebob Movie: Sponge Out of Water also remains unchanged at three.

Kevin Costner's new Disney film MCFarland, Usa enters at four and high school comedy The Duff is new at five.