Oh I see, is it Swedish by any chance? I think they had tins of that on Top Gear recently.
It is.
Northern part of Sweden, Baltic coast around 63° N. The "High Coast" as it is called, because it is an archipelago with steep islands. They couldn't afford salt for their herring, so undersalted, and the result was fermented. It really stinks but the taste is much better than the smell. The trick to minimise inconvenience is to park your trebuchet, but stay outside, and get a bucket, fill it with drinking water, and open the can under water. This will contain
The Spray and allow you to pick the filets out as cleanly as possible.
Traditionally, the fish is served with a thin soft or crispy bread called Tunnbröd (lit. "thin bread", "dünnes Brot") that looks like a large square tortilla but is made from wheat and rye, Swedish peanut fingerling potatoes, and chopped red onion. Vodka or even better, Aquavit, is IMNSHO a required drink, and it is recommended to have beer available too. Some connoisseurs require milk instead of alcohol. I can't even drink milk to unfermented fish, so I'll stick to the Aquavit.
That is, if I ever try it again. I think that once is enough, and since I remember the smell even now, 30 years later, I see no need to repeat the test.
I also got very sick, but I think the vodka can have played a part in that.