Not really to do with the business of writing, but PG’s fleeting attention was captured by the title of the OP.
From The London Review of Books:
In 1584, as Ivan the Terrible lay dying, he called from his bed for his unicorn horn, a royal staff ‘garnished with verie fare diamondes, rubies, saphiers, emeralls’. Unicorn horns were believed throughout Europe to have magical curative properties; as late as 1789, a unicorn drinking horn was used to protect the French court, where it was said to sweat and change colour in the presence of poison. To prove the horn’s efficacy, Ivan ordered his physician to scratch a circle on the table with the tip of the horn, and to ‘seeke owt for som spiders’. The spiders placed within the circle curled up and died; spiders placed outside it ran away and survived. The dead spiders, though, could not console Ivan. ‘It is too laite,’ he said, ‘it will not preserve me,’ whereupon, soon afterwards, he died.
The unicorn horn was, of course, a narwhal tusk: the tooth of a small Arctic whale, which grows out through the upper lip, twisting counter-clockwise for up to 2.5 metres. Named rather ungallantly for the Old Norse word nar, meaning ‘corpse’, and hvalr, ‘whale’, after their mottled grey markings, narwhals are unicorn-like not just in their appendages, but in their elusiveness; they are one of the mammals about which we know least. They spend the winter months dodging dense pack ice, where humans cannot follow, and can swim a mile deep, twisting upside-down as they descend into pitch-black water.
. . . .
The great mystery of the narwhal is the purpose of its tusk. Appearing in males of about a year old, as short and thin as a little finger, it grows for nearly ten years until it’s as wide as 25 cm at the base. Herman Melville writes of the ‘nostril whale’ in Moby-Dick: ‘Some sailors tell me that the Narwhale employs it for a rake in turning over the bottom of the sea for food. Charley Coffin said it was used for an ice-piercer … But you cannot prove either of these surmises to be correct.’ He ends by suggesting it would make an excellent letter opener. Because less than 15 per cent of female narwhals have the tusk, it can’t be necessary for survival, and so, when male narwhals were observed clashing tusks it was often interpreted as rivalrous jousting. Recently, though, scientists have found that the tusk is shot through with around ten million nerve endings, and by rubbing tusks on meeting, the narwhals may be passing on information about the salinity (and therefore propensity to freeze) of the water through which they have just passed; not aggressors, then, but Mercators.
. . . .
The legend of the narwhal is not a gentle one. The Danish ethnologist Knud Rasmussen recorded the myths of the Inuit of Greenland’s northwestern coast in the late 19th century. In the narwhal origin myth, the cruel mother of a blind son tricks him out of his fair share of bear meat. The mother plaits and twists her hair into a long braid and the two go out to harvest passing white whales; the son binds her with ropes to one of the whales, and it drags her into the sea. According to Rasmussen, ‘she did not come back, and was changed into a narwhal … and from her the narwhals are descended.’
. . . .
This was not Elizabeth I’s only narwhal tusk. Sir Humphrey Gilbert, Walter Raleigh’s half-brother, presented her with a gem-encrusted narwhal tusk worth £10,000 (enough, at the time, to buy and staff a small castle). It was, he told her, a ‘sea-unicorn’.
Link to the rest at The London Review of Books