Scotty switched the light off and they sat down on the hard rock floor. Rick closed his eyes and breathed deeply. Plenty of hard work ahead. He might as well rest while he could.
Scotty spoke suddenly. "Plenty of good fresh air down here. Isn't that a little odd?"
Rick stirred. "Is it? I hadn't thought much about it. But I suppose the air ought to be stale and smelly."
"Wet your finger."
"Huh? Oh, okay." It was the ancient trick of using the cooling caused by evaporation of moisture from a damp finger to show the movement of air currents. Rick let out an exclamation. The air in the tunnel was in motion!
Scotty said with suppressed excitement, "Close your eyes. I'm going to light a match."
Rick did so, and saw the light even through closed eyelids because his pupils were fully dilated. He opened his eyes cautiously, squinting against the glare of the match. As the pupils contracted he saw that the paper match burned brightly, and that the flame flickered!
Scotty jumped to his feet, switching on the flashlight. "The breeze is coming from the slide!"
With one accord they rushed to the slide and began pulling rocks away. Clearly, the tunnel sloped upward at this point. The question was, did it emerge in a real opening, or only in a hole driven through for ventilation?
There was only one way to find out: move rock!