Brandishing a narwhal tusk to fight the London Bridge terrorist.

The terrorist was armed with a knife, and the narwhal tusk was 5 feet long, I'm reading in "Narwhal tusk and fire extinguisher used to tackle London Bridge attacker/Members of the public, including a convicted murderer, bring terrorist to the ground" (The Guardian).

Scotland Yard is investigating how 28-year-old Usman Khan was able to launch the attack in London Bridge, despite being known to the authorities and fitted with an electronic tag to monitor his movements. He was allowed out a year ago after serving time for his part in a plot to blow up the London Stock Exchange.

In footage that has since emerged, Khan is sprayed with a fire extinguisher, while another man tries to suppress the assailant with a narwhal tusk – a long pointed tooth from a type of whale – lunging at him. It is believed the item was pulled from the wall of Fishmongers’ Hall, a grade II-listed building on London Bridge, by a Polish chef called Lucasz....

ADDED: I'm re-reading "Moby-Dick," so let me give you the chapter on the narwhal:

Narwhale, that is, Nostril whale.— Another instance of a curiously named whale, so named I suppose from his peculiar horn being originally mistaken for a peaked nose. The creature is some sixteen feet in length, while its horn averages five feet, though some exceed ten, and even attain to fifteen feet. Strictly speaking, this horn is but a lengthened tusk, growing out from the jaw in a line a little depressed from the horizontal. But it is only found on the sinister side, which has an ill effect, giving its owner something analogous to the aspect of a clumsy left-handed man. What precise purpose this ivory horn or lance answers, it would be hard to say. It does not seem to be used like the blade of the sword-fish and bill-fish; though 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; for the Narwhale, rising to the surface of the Polar Sea, and finding it sheeted with ice, thrusts his horn up, and so breaks through. But you cannot prove either of these surmises to be correct. My own opinion is, that however this one-sided horn may really be used by the Narwhale—however that may be—it would certainly be very convenient to him for a folder in reading pamphlets. The Narwhale I have heard called the Tusked whale, the Horned whale, and the Unicorn whale. He is certainly a curious example of the Unicornism to be found in almost every kingdom of animated nature.

From certain cloistered old authors I have gathered that this same sea-unicorn's horn was in ancient days regarded as the great antidote against poison, and as such, preparations of it brought immense prices. It was also distilled to a volatile salts for fainting ladies the same way that the horns of the male deer are manufactured into hartshorn. Originally it was in itself accounted an object of great curiosity. Black Letter tells me that Sir Martin Frobisher on his return from that voyage, when Queen Bess did gallantly wave her jewelled hand to him from a window of Greenwich Palace, as his bold ship sailed down the Thames; "when Sir Martin returned from that voyage," saith Black Letter, "on bended knees he presented to her highness a prodigious long horn of the Narwhale, which for a long period after hung in the castle at Windsor." An Irish author avers that the Earl of Leicester, on bended knees, did likewise present to her highness another horn, pertaining to a land beast of the unicorn nature.

The Narwhale has a very picturesque, leopard-like look, being of a milk-white ground color, dotted with round and oblong spots of black. His oil is very superior, clear and fine; but there is little of it, and he is seldom hunted. He is mostly found in the circumpolar seas.