Willard glanced at Connelly, who had moved closer to speak to him, but had never taken her eyes off the cave entrance.

"Methane gas, as you know, is in abundance around cow farms," Connelly said. She paused and met Willard's eyes. Satisfied that he was listening, she continued. "But it's not the cow feces itself that creates the gas…it's the breakdown of organic material within the manure. This doesn't just happen with cow poop, either. You just notice it because of the high concentrations on most farms."

"Ok, fine," Willard said. "Maybe these caves are filled with methane escaping from the ocean's decomposing organisms. Fish poop, too. And don't volcanoes on Earth spew methane? It could be a naturally occurring gas here."

Willard noticed Robert pause his slow creep toward the cave entrance. "He does have a point."

Connelly nodded. "I'm sure some of the gas comes from natural sources, but the concentration of methane is high enough to suggest otherwise." Connelly switched on her PMS suit's headlamp and aimed it toward the cave. The gentle mist in the cave glowed brightly in the light. The entrance tunnel was empty. She turned to Willard again, lighting up his face. "Methane is created by the decomposition of organic material, any organic material."

"Which means that these caves could be filled with little alien rats or some kind of fungus," Willard said.

Robert looked back, shaking his head. "Nope."

"Why not?"

"Too much gas." Robert said. "The amount of organic material somewhere in this cave system must be immense, suggesting a significant population of larger creatures, probably of varying sizes, both plant and animal."

"But this cave is barren, Willard said. "There's nothing here."

Robert smiled. "You've been caving, right?"

Willard didn't want to answer. Robert knew the answer anyway. "Yeah."

"Would you say some of those caves were devoid of life?"

Willard sighed. "I came through about ten different tunnels before I made it to you two. I didn't see anything on the way."

Connelly looked at Willard with a shocked expression. "How did you find us?"

Willard sighed again. "I don't know. All I know is that we need to get the hell out of these caves and back up to the surface."

The seriousness in Willard's voice garnered him the attention of both Robert and Connelly. They stared at him, waiting for him to say more. But that's all he had. Something inside him was urging, pushing him to leave. The message was simple: run!

"You feeling okay?" Robert asked.

"I'm fi—" A shadow slid into the cave entrance. Willard blinked and the shadow slipped away.

Robert and Connelly spun towards the entrance. "What is it?" Connelly said.

"What'd you see?" Robert asked, his voice pitched higher than normal.