I didn't mean to sound so harsh there BarBar, lol.
I do know what you're getting at, but I've always liked to think that although Han realised that there was something amiss, Leia (who said the line) had never encountered such an entity as this in her experience before, and simply didn't really register / comprehend that those were actual gigantic teeth in the distance, of some monstrous worm they were now inside of, rather than just the asteroid cave they initially entered....
Hope that helps a little. I'd rather keep the teeth though, than have a 'gumsy' worm, regardless of that line.