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The Flight of Dragons? (the book that The Flight of Dragons is based on)
They eat limestone to produce hydrogen gas for their fire breathing. I vaguely remeber a live-action TV show about some children finding a dragon in modren times that could be an adaption that had a similar explanation for fire breathing.
Edited by jormis29
The "How To Train Your Dragon" animated movie series has a dragon species like this and they were adapted from a book series, so maybe that?
was it a story or more like a mocumentary (for lack of a better word) book about dragons
Edited by Bootlebat
Dragonology or The Dragonology Handbook?
I second Dragonology. I remember reading a section just like that.
Mentioned as the mechanism by which dragons produce fire in one of the Knightmare novella/game books (the first I think).
Flight of Dragons suggests a flint, and then rejects it in favour of chemical ignition, IIRC.
The dragons in the GrailQuest choose-your-own-adventure books have crystal and metal on their front teeth to ignite the methane generated by eating chestnut leaves.
It looks like variants of this idea are quite common, I'm afraid...
Edited by DaibhidC
I read it when I was a kid and it's always bugged me. It has dragons who breath gas and strike something like a flint on their tongue/back of mouth or throat to make a spark and that's how they breath / make fire.