You find a dead raw fish on the beach, you eat it. Fun surprise, it had eggs - when you die a Horrid Tentacle spawns from your body.
Eating Raw Fish has some percentage chance of giving you hidden status effect Riddled with Worms which triggers on your death.
Similar to Plague Rat attacks that successfully roll Minor Poison have a subsequent 50% chance to apply a hidden Status Effect of Shambling Infection.