How does the Great Goblin react when he discovers Thorin's sword? Why?

Thorin explains that they are going to see relatives on the East side of the mountains. Other goblins say that a bolt of lightning struck some of their comrades and Thorin's sword is also indicative of his anti-Goblin intentions. The sword is called Orcrist, Goblin-cleaver, but the Goblins call it Biter.