The Bible is often criticised as a "book of fairy tales", with its mention of even fire-breathing dragons being used as proof of this. But when we get past the initial mockery and start actually thinking about what we're reading, what we notice is that none of the animals we read about in the Bible are particularly unusual. Some of them are unique, such as "the chief of the ways of God" Behemoth (Job 40:15-24). But is that because it's mythical, or just because it's bigger than any other land animal? One way or another, something is going to be the biggest land animal on earth, and since we're not particularly big ourselves, we're going to find these things quite spectacular.
And that is rather the point of God making such spectacular creatures. As He did in Job, He made them to show off; both to display His power and sovereignty, and even to humble us, reminding us of our own place in His creation. This is the precise way He uses the fire-breathing Leviathan just one chapter later. In Job 41:18-19, we read that Leviathan's sneezings flash forth light, and burning lights proceed from his mouth.
Now of course, there is the possibility of poetic embellishment here. After all, the same verse describes Leviathan's eyes as "like the eyelids of the morning", though of course, the morning has no eyelids. So it's quite possible, likely even, that Leviathan didn't literally shoot fire. But whatever is happening here can be poetically described as shooting fire.
But this does sound rather like a fairy tale, doesn't it? Fire breathing dragons? Throw in a knight on a white horse bidding for the attention of a princess and you have a traditional tale right there! But here's a question to ask: By what logic do we assume none of these tales are based on a real occurrence? That would explain why so many isolated cultures not only describe remarkably similar dragons, but also ones that at least somewhat match what we now see in the fossil record. In fact, this is such a prominent phenomenon, even Carl Sagan presented a theory in which our ancestors, while they didn't see real dragons, somehow inherited memories from our previous ancestors millions of years ago. So it's not that they saw dinosaurs, it's that the creatures they evolved from did, and just passed that down.
But it's sort of easy to imagine, especially given the large reptiles we still have with us today, that maybe our ancestors saw a Komodo dragon, or a large crocodile, and that's what they called dragons. But fire? Well, it turns out, that's not hugely unrealistic either. In fact, there are many extant animals that even today utilise volatile chemical defences. Take, for example, the bombardier beetle.
The bombardier beetle has a particularly interesting defence. The bombardier beetle stores two chemicals, hydroquinone and hydrogen peroxide, in two separate reservoirs inside the abdomen. When threatened, and in some cases even when swallowed, the beetle sends these chemicals to a special chamber, along with a special enzyme, triggering a chemical reaction, heated to up to 100°C, which it swiftly fires at its target like a boiling water pistol.
The bombardier beetle is not alone. A great many animals use chemical reactions for similar purposes. The electric eel is another, likely more familiar example to most readers. If these did not exist, and the Bible mentioned eels that could bring forth enough lightning to kill a crocodile, I have no doubt skeptics would also criticise the Bible for these "mythical" fish.
But God is a master designer with no respect for man's hubris. If He wants to make a burning beetle booty, He can make a burning beetle booty. If He wants to make a thunder fish, He can make a thunder fish. But what about fire breathing dragons? Consider this: Many prehistoric reptile skulls contain mystery cavities, which aren't likely connected to the respiratory function. While we cannot be certain, it is also not reasonable to dismiss the theories that some of these cavities could have been used as chemical storage and delivery systems, producing, if not actual fire, an effect which can be reasonably described as fire.
Given that there are, indeed, modern animals which use intricate chemical systems to produce amazing effects, it is not unreasonable to believe that legends ascribing fire breath to large, dinosaur-like reptiles are based on a reality observed by our ancestors. It requires personal incredulity, and even a little circular reasoning, to dismiss it out of hand. Personally, I prefer to keep an open mind. Since there is ample evidence that Jesus really is the risen Lord, I am especially inclined to believe His book.