The thundering roar turned a large part of the forest upside down. Small and large animals had stopped whatever they were doing and rushed off to the alpha beast's call. Their whole existence had lost any meaning. Protecting their master was the only thing that mattered.
It shocked Kyon to the core. Instead of running away as a normal person would do, he rushed to the source of the roar that was only ten kilometers away, right in front of him. He could easily avoid unpleasant surprises with the help of his flying spies, so it was only reasonable to investigate the situation. That's how he justified his immense curiosity.