Dragon Flower

S1, E9: Trader Johann comes to Berk, bringing with him new and exotic goods that the people of Berk hurry to trade for. But soon, the dragons begin sneezing and getting sick. Hiccup, with the help of the others, determines that the dragons have been poisoned from eating the Blue Oleander flowers that have been growing throughout the village. The only cure: the venom of the Scauldron, a massive and vicious sea dragon.