Rotten fish in pickle. Nothing more, nothing less.
Being one of the most succesful exports of Sweden, Surströmming is probably the most disgusting canned fish mankind ever made. During the dark and bloody ages of the feared Vikings, when refridgerators did not even exist as blue prints, the babaric nords tried to prevent fish from rotting by putting it into salt water. Since proper cooling was not a given, it was kind of a brilliant idea to catch fish - which were living in salty sea water - and put it into water that contained even more salt to keep the fish fresh.
As the nordic settlers where literally swimming in fish, they somehow liked the smell that dead and rotten fish produces. To keep this smell and cold taste as close as possible to the original, the head, eyes and bones were not removed before conserving the fish in salt. As a positive side-effect, Surströmming turned out to be a perfect protection against any type of mosquitos.
It is said that Surströmming can make one throw up only by its smell. As opening a can of Surströmming in public transport or inside airplanes is considered a criminal act, some of the Swedish players were sent to Exile because of Surströmming.