Three whiskered, weather-beaten men stand facing each other, alone in a huge cemetery. They exchange suspicious glances and remain almost perfectly still, not saying a word. The stare-off continues for two and a half minutes.

Not exactly the stuff of interesting cinema, is it?

Actually it's one of the most riveting and acclaimed feature film sequences of all time: the climactic showdown at the end of Sergio Leone's The Good, the Bad and the Ugly.

This year marks the 50th anniversary of the film’s original release. In the five decades that have followed, it has had a huge impact on cinema and popular culture.