It’s a fact of life that there are times when the shadow can be mightier than the substance.

Over ninety years ago the German film-maker F.W. Murnau chilled cinema audiences with the 1922 silent movie, Nosferatu.  It’s still chilling people today, and probably the creepiest scene of all is where the vampiric  Count Orlok steals up the dark stairway, only his shadow visible on the wall.  Thus sparking off a tradition that was to go from Hammer to Twilight, and provide a stream of starring roles for actors capable of turning on sinister charm at the drop of a garlic clove.

In the 1960s film-makers again became aware that what you don’t see is often scarier than what you do.  Anyone who watched Hitchock’s The Birds will remember how menacing it was when ordinary birds began to gather on rooftops.   And with Roman Polanksi’s Rosemary’s Baby, did we actually see the demon who attacked Mia Farrow?  My memory is that we didn’t, although it’s always possible I had gone out to buy the popcorn at that point.

Fiction writers have always known that what you don’t see can be a whole lot scarier than what you do see, but sometimes there’s an irresistible temptation to add that last swish of the knife, to include that extra sentence describing the corpse – and to apply just one more turn of the screw.

The famous and exclusive Detection Club, (think Dorothy L. Sayers, Agatha Christie, G.K. Chesterton), reportedly required (and indeed may still require), its members to take an oath, part of which warns them to avoid: ‘Sinister Chinamen,’ (doubtless a sly nod there to Sax Rohmer, creator of the Fu Manchu books), as well as ‘divine revelations, and poisons unknown to science’.  The oath also apparently forbade members to purloin other people’s plots, ‘whether under the influence of drink or not’, but that’s probably another story.

Translated into a warning to writers of pyschological thrillers, this oath might read:  ‘Let there be no superfluity of splattering gore, no unnecessarily-festering corpses, no wild-eyed axe-killers or gibbering maniacs springing out of cupboards.  Instead, let there be the midnight creak on the stair, the whisk of something sinister disappearing round a corner, a glimpse of the shirt-tail of a ghost rather than a glimpse of the ghost itself…’       And let the chills be understated, and let the reader’s own imagination fill in the blanks.

Because it’s another undoubted fact that radio has some of the best pictures.