Four goblin faces with their tongues touching- creating a vortex of malevolence. I don't suppose it means anything. I think it's just the mason having fun.
Norwich cathedral is rich in medieval survivals. It probably helped that Norfolk is so far away from everywhere else. Like Lancashire and Sussex- two other out of the way counties- it retained its catholic sympathies (they're still strong today) and the iconoclasts (with their Bibles in their boots) were unwelcome and worked without encouragement and were therefore less thorough. We were in Peterborough Cathedral on Monday- a similar building of a similar vintage- but in the East Midlands- which were the Puritan heartlands- and it got much more radically smashed up. For starters the cloisters have gone- and their bosses with them. Actually, it's a wonder it survived at all- because it was an abbey church- and could have gone the way of most of the others- only its abbot was a canny man who managed to get on the right side of Henry VIII. Seeing that dissolution was inevitable, he lobbied for his church to become a cathedral- and Henry said "What a good idea- and why don't you be its first bishop?" Lucky man; many of his peers wound up on the scaffold. Perhaps he was not merely canny, but charming.