— Hiccup and Astrid had not noticed the lens that was on Heather's belt
In "Sins of the Past", the Dragon Hunters have possession of the Dragon Eye, and as their new leader, Krogan is determined to get a hold of the lens that Heather wears on her belt. He manages to get her to trade it for her dragon Windshear. Turns out, the Riders had never noticed it on her belt even after so much time they spent together, neither did Heather realize what it was after watching the Riders work with the Dragon Eye and the other lenses during that time. Now everyone is curious about what info it contained, but it's in Krogan and Viggo's hands. It is uncertain how exactly Krogan knew Heather had it to begin with, though it is suggested Johann was the only one to ever notice it and then passed that info onto Krogan and the Hunters, hoping it will lead them to the "King of Dragons."