Get your clothespins ready, it's Surströmming Day! For the uninitiated, that means we're in Sweden and cracking open this year's surströmming harvest to enjoy its putrid wonder. Surströmming is Baltic herring that's been caught in April and May, then lightly salted and allowed to ferment. Beginning in the 1940s, a royal ordinance forbade the selling of Surströmming before the third Thursday in August to prevent incompletely fermented fish from being sold. The ordinance is no longer on the books, but the tradition holds.