Hypothetically, how much do you think a (fictional) dragon eats?

[Coluber42]

I tend to assume that a dragon should be more akin to a bird than a reptile, personally. Scales and feathers are not all that different. Lighter bones, frequent diet of relatively small items... now, I don't assume that the 'fire breathing' would require a higher internal temperature. More likely an arrangement somewhat like the ability to spit venom. Possibly containing a substance that ignites on contact with oxygen, if fire is really necessary, but more likely a type of venom or highly acidic toxin. Disable your prey, and start the digestive process at the same time.

Or fire breathing could be accomplished by ejecting two"venoms" that combust when they mix. The Vernon ducts could then be aimed such that the two streams would actually combine a safe distance in front of the dragon's mouth. That would not only remove the requirement for a high internal temperature, but also reduce the need for as much thermal shielding or internal organs capable of withstanding high temperatures. Maybe that's an adaptation of dragons from regions without enough knights in steel armor.

It would, however, mean that certain types of injuries to the mouth, teeth, fangs, etc, could conceivably make the dragon's head explode.

Terry Pratchett's swamp dragons can breathe fire because of the volatile stew in their stomachs, but are rather prone to digestive difficulties of an explosive nature.