Dragons have soft underbellies, the Storyteller on the telly says. The wise ones cover their vulnerability with an armor of glittering gems and shining gold. Of course, gold is a soft metal and it is very heavy. But the wise dragons use it because they know, without it, they are mortal and can be killed.
But a dragon who armors his belly must be careful to cover all of it. He must not leave one spot uncovered. If he does, all his work is for naught.
All it takes is one weak spot, on the left side, over the heart.