When most people browse websites the chances of interruption (from colleagues, kids, the phone, email, IM, TV in the background) are high, and this reduces the amount of brain power available to them.

"Watch an evening's worth of TV and count how many times you hear music in the background," says Jeremy Lascelles, chief executive of Chrysalis.

Being part of the background in a convincing (令人信服的) way is challenging, and being on a film or TV set is always fascinating.