A typical gurn might involve projecting the lower jaw as far forward and up as possible, and covering the upper lip with the lower lip, though there are other possibilities.
In the UK, contests to climb a greasy pole were held at numerous fairs including the Crab Fair in Egremont, Cumbria where the contest continues to this day - alongside the annual Gurning World Championships see Gurn.
Images included a gull coming into land, a tree frog jumping through the air, a man gurning, and the end credits of the film Carry On Cowboy.