Of course these aren’t dragons. No, they are uglier. They are saurians, more like Tyrannosaurus rex than anything else — big hindquarters and heavy hind legs, heavy tail, and smaller front legs that they use either in walking or to grasp their prey. The head is mostly teeth. They are omnivores whereas I understand that T. rex ate only meat. This is no help; the dragons eat meat when they can get it, they prefer it. Furthermore, these not-so-fake dragons have evolved that charming trick of burning their own sewer gas. But no evolutionary quirk can be considered odd if you use the way octopi make love as a comparison.
[...]
“They don’t exactly breathe fire. That would kill them. They hold their breaths while flaming. It’s swamp gas — methane — from the digestive tract. It’s a controlled belch, with a hypergolic effect from an enzyme secreted between the first and second rows of teeth. The gas bursts into flame on the way out.”
[...]
There are only four places to put an arrow into a Nevian dragon; the rest is armored like a rhino only heavier. Those four are his mouth (when open), his eyes (a difficult shot; they are little and piggish), and that spot right under his tail where almost any animal is vulnerable.
[...]
The dragon was weaving its head back and forth and I was trying to weave the other way, so as not to be lined up if it turned on the flame — when suddenly I got my first blast of methane, whiffing it before it lighted, and retreated so fast that I backed into that baby I had stepped on before, went clear over it, landed on my shoulders and rolled, and that saved me.
I doubt I caught this the first time I read the book, but this time I immediately noted that methane is a colorless, odorless gas:
The familiar smell of natural gas as used in homes is achieved by the addition of an odorant, usually blends containing tert-butylthiol, as a safety measure.
I suspect someone caught this detail in one of his early drafts, because Heinlein addresses it:
The reason that I backed away in time was halitosis. It says here that “pure methane is a colorless, odorless gas.” This G.I.-tract methane wasn’t pure; it was so loaded with homemade ketones and aldehydes that it made an unlimed outhouse smell like Shalimar.
[...]
A proper dragon, with castles and captive princesses, has as much fire as it needs, like six-shooters in TV oaters. But these creatures fermented their own methane and couldn’t have too big a reserve tank nor under too high pressure — I hoped. If we could nag one into using all its ammo fast, there was bound to be a lag before it recharged.
I had heard the western genre referred to as horse opera before, but oater was new to me.
“Oater” is a common solution in the world of crosswords.