Berk's Forumvine

Headcanon: Injury Logistics (Feel free to suggest a better term.)

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Dragons (wild ones especially) have an extremely good grasp on extent of bodily damage, and if a limb becomes injured beyond repair, they may just amputate it with their own teeth.

Headcanon: Levels of Reasoning

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Dragons have different "levels" of conscious reasoning that they can operate in. There's the "high" level, the usual, in which their minds operate... not quite like a human's, as they're still wild animals, but similarly. In this "level", they are capable things like logic, thought, emotion, overriding instinct, etc.
Then there's the "low" level, in which their minds operate purely as a wild animal, fully instinctual, basically "my senses are my world". This "level" is typical of very hungry dragons on the hunt, or of dragons in heat.

There's also something of an in-between "level", in which they may use some higher reasoning (like drawing parallels between the way different scents in an area are linked and the way a spider's web is constructed), but definitely not operating emotionally.

Headcanon: Spatial Concerns

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Dragons don't like cramped spaces, and in general, will not willingly enter/traverse any place where they cannot fully spread their wings without brushing against something. Interesting to consider that this makes the plight of the Dragon Hunters' caged dragons much, much worse.