In The Empire Strikes Back Han dives into a cave in an asteroid to escape the Imperial ships chasing the Millenium Falcon. Originally I was wondering why there was air available to them outside of the ship, as well as heat, but this article about the exogorth explains that.
But it leaves open another question: Solo flies the ship into a cavern. Assuming he doesn't notice the teeth at all, there's another issue. While Han Solo is brash and quick acting and appears reckless, he does keep track of all the factors in a situation, which is how he can often react quickly and succeed with moves others would consider reckless.
So he flies the ship into a cavern. Once he's in this cave in an asteroid, there's heat outside and an atmosphere (again, explained in the article above). When they wonder about the rumbling, they exit the ship with only breathing masks.
Why isn't an experienced pilot/captain/shipowner like Han alerted because there's an atmosphere and heat outside the ship when he's on an asteroid in the middle of space? Granted, the cave is safer than facing several capital ships, but even if he didn't believe in the slugs, shouldn't he have started putting the facts together from the start?
I know the article says he doesn't give much credit to the stories of exogorths, but wouldn't atmosphere and heat in such a cave be some form of a warning? And even if he's not sure, why do something like shoot the slug (whose mouth you're in) in the tongue? Obviously at some point before he starts flying out, he's beginning to give the tales some credit.
Is there an in-universe explanation for why he'd ignore all these factors (and still fire his blaster into the exogorth's tongue!) or is his carelessness nothing more than a function of plot?