Sigurd listens closely to Kol and he finds that it's true. He can hear every heartbeat. It takes a moment to focus on just his oldest brother's. Then Kol is moving and Sigurd sees what he's about to do and he almost protests out of a habit -- or something -- maybe he's afraid of getting Ubbe hurt seriously but Ubbe is steadfast, as always.

The hunger demands to be satiated and the scent of fresh blood right there makes it impossible to ignore as he near instantly moves forward and all thoughts of worry over Ubbe's safety are blurred into the background.