The franchises where sequels equal box-office bonanzas

When a movie franchise with genuine cultural heft releases another instalment – The Bourne Legacy, say, or Terminator: Salvation – the world takes notice. But then there are the unlikely money spinners, the genre titles that spew a sequel every year or so, making a profit with little impression on the popular consciousness.

This week a new trailer was released for Paranormal Activity 4, the latest in a line of profitable micro-budget horror flicks. The gruesome, cheap, bizarrely box office-friendly Saw series boasts seven films. The latest in the (surprisingly satisfying) Fast and the Furious franchise, Fast Six, is in production now, with a seventh under discussion.

Who's watching them? Enough of us, apparently.