After five or ten minutes of what I thought was a serious conversation, Roger cut it off and got to the point.

Two volunteers cut off from the rest world for eight months stepped out on a mock-up of Mars on Monday, reaching the dramatic half-way point of their experimental "voyage" to the Red Planet.

But I think there may be something of a cut-off point when it comes to what are called "social networking" websites such as Facebook and, more especially, Twitter.