Reece Shearsmith’s severed head lies on a purple cushion, eyes open, mouth gaping. The actor and writer’s bonce is a prop from the 2018 Inside No 9 Halloween special in which he and Steve Pemberton play themselves in a live broadcast that goes eerily wrong, as malevolent ghosts invade a TV studio. It’s exhibited here not as a joke, or a curio, but as a relic of idealism. Fans of the black comedy Inside No 9 will know its creators have a real passion for horror, fully shared by this witch’s cauldron of an exhibition.