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Rakfisk is a traditional Norwegian dish, which is made by burying trout or char in the ground for several months, and then eaten without cooking. It is traditionally eaten around Christmas, but it is not a specifically Christian tradition (any more than turkey or mince pies). Since it is eaten at Christmas, the burying would have to have happened several months before, unless the fish is buried for an entire year. Norway is not a particularly Catholic country, so it is unlikely to have been a Catholic tradition.