Complex sentence: Realizing that Gobber was telling the truth about the Boneknapper all along, the gang have to take shelter inside their own trap, and all seems lost until Hiccup sees an empty spot on the dragon's neck armor that exactly resembles Gobber's belt buckle bone.
Split into simpler sentences: Realizing that Gobber was telling the truth about the Boneknapper all along, the gang have to take shelter inside their own trap. All seems lost, but Hiccup sees an empty spot on the dragon's neck armor that exactly resembles Gobber's belt buckle bone.