Tragedy struck London yesterday when an attacker wearing a fake explosives vest killed two people with a knife on London Bridge before he was shot and killed by police. It is an absolutely terrible thing to have happened in one of the world's most wonderful cities.

One aspect, however, does serve to show how Great Britain can easily nurture the imaginations of a J.M. Barrie, J.K. Rowling or Neil Gaiman. Before the killer was ultimately brought down, he was subdued by a man wielding a five foot narwhal tusk. (Another man used a fire extinguisher as a makeshift weapon.)

The Internet, looking for any aspect of mirth to cling to in a world gone mad, is, understandably, going slightly gaga for the narwhal tusk. Separating fact from rumor can be confusing, so we're here to answer your basic questions about this perplexing situation.

Remind me what a narwhal is?

Basically a sea unicorn. The average one weighs between 1,760 and 3,530 lbs and can live up to 50 years. Its tusk grows through its upper lip forming a helix spiral. Usually only male narwhals grow a tusk, but about 15 percent of females do, too. Male narwhals touch their tusks to exchange information about water conditions, similar to a trucker's use of CB radios.

Okay, so who is this guy with the narwhal tusk?

So far he is only known by one name, Łukasz. It might be his first name, it might be his last name, or maybe it's like Cher. Łukasz is a Polish immigrant who, along with other brave people, raced toward danger when he saw a man with what appeared to be an explosive vest.

How did he get the narwhal tusk?

He got it from work.

What?

He took it off the wall at the events space where he worked.

What the heck kind of events space has a narwhal tusk on the wall?

Fishmongers' Hall.

Fish-WHAT? What is that? That sounds gross.

No, not at all. It extends from Britain's centuries old guilds, more social clubs and charity organizations these days than anything else. Fishmongers' Hall is a gorgeous structure built in 1834 right along the Thames. The original on that site, built in 1414, burned in the Great Fire of 1616. Another from 1671 was torn down to make way for London Bridge in 1827.

A conference concerning criminal justice was being held at the hall, and that is believed why the the attacker, an ex-convict, was there prior to his rampage. It's also why a convicted murderer named James Ford aided Luckasz in bringing the stabber down.

I don't know if I can process that last bit, but let's stick to Fishmongers' Hall. Are there other weird clubs in London like this?

Indeed there are. The livery companies, as they are called, are guilds that go back to the 14th century. In addition to The Worshipful Company of Fishmongers there's The Worshipful Company of Drapers, The Worshipful Company of Wax Chandlers, The Worshipful Company of Cordwainers, The Worshipful Company of Joiners and Ceilers, The Worshipful Company of Makers of Playing Cards and many others. 110 in all.

I find this charming.

Other European places have this sort of thing, too. In Zurich there's the Vereinigte Zünfte zur Gerwe und zur Schuhmachern.

I feel like that's maybe where Santa's elves live.

Perhaps.

Will Łuckasz get the tusk to the city?

Hopefully, yes, but a replica.