There are two types of fear, the fear that bites and the fear that creeps. Nathan Bland, the teenage protagonist of the horror story that David Mitchell recently published on Twitter, has had a strong dose of the first. He’s been mauled by a bull mastiff, which ‘pulled skin off my cheek like skin off roast chicken' and 'shook me like a doll, my own blood blinding me'. The dog still stalks his dreams. When Nathan and his mother arrive at the house of Lady Briggs, an aristo his mother is keen to impress, a dog barks and he feels a pang of terror - ‘my lungs fill with dark’ – before he realises that it’s ‘only a little yappy thing’. Later, Nathan plays a game of ‘Fox and Hounds’ with Lady Briggs’s creepy son Jonah. He’s running, trying to catch Jonah up, when he hears the mastiff behind him. Suddenly it appears with Jonah’s bloody head dangling from its jaws. Nathan runs into Lady Briggs’s house, slams the door and blames the apparition on the Valium he took earlier.

But the fear that bites was just a warm-up. Towards the end of the story, Jonah – I don’t want to give too much away but he gets much creepier – tells Nathan that the mastiff experience was just to soften him up, ‘like your butcher tenderises meat – by fear’. But by now the fear that bites has given way to the fear that creeps, and Twitter turns out to be well suited to conveying it. Dread is all about information, released slowly, which is what Twitter does, especially in its role as news-breaker. One tweet tells us that something dreadful may have happened; we sit in front of our screens waiting for an update, then another tweet reveals that the situation is worse than we thought, and we sit tight for more information as the fragments slowly add up to a picture of horror. Mitchell exploits this familiar experience brilliantly.

As the story reaches its climax, time slows down. In the story’s first three tweets, posted early on the morning of 14 July, quite a bit happens. Nathan and his mum get off a bus, walk down the road past a pub, and we learn all kinds of things about their characters: that his mum has anxiety about their class status, that she’s divorced his dad and he’s late with the alimony, that Nathan is good at being cheeky. Later, on 19 July, it takes Nathan 15 tweets to walk up a staircase, and as time slows down to this dreadful pitch we learn that Lady Briggs and Jonah – wait for it – control time. In other words, Mitchell uses Twitter to draw attention to the control he has over time and suspense at the same time his character realises – or doesn’t quite realise; he blames the Valium to the end – that he is himself being authored. Whether or not he escapes from the mastiff has nothing to do with how fast he can run, and everything to do with the whims of the people writing his life and their desire to make him suffer. The fear that creeps is the gradual recognition of helplessness.