After the rat swarm retreated, the strange tapping sound of "thump... click... thump... click..." did not stop. Instead, it became clearer and more rhythmic, as if a giant, old mechanical heart was slowly beating in the depths of the earth.
This eerie sound cast a new shadow over the hearts of the group, who had just achieved victory.
"What the hell is hiding down there?" Chen Shouzhou lay at the scorched entrance of the tunnel, listening intently, his brows tightly furrowed.
"It sounds like... the circulation pump or piston of some large-scale equipment," Lin Mo, who was usually taciturn, stepped forward, his expression exceptionally grave. "And this kind of low-frequency mechanical resonance is definitely not something ordinary civilian equipment can produce."
A sense of doubt rose in Chen Shouzhou's mind. He knew that not figuring out the source of this sound was like burying a time bomb in his own home, ready to explode at any moment.
He made a decisive call: they would organize a tunnel exploration mission. This hidden danger had to be completely rooted out.
"Old Li, Old Lin, you two stay and guard the warehouse. Be on alert," he quickly assigned roles. "Dr. Su, you're on logistics and medical support, ready to assist at any time. A'Jie, you're coming down with me. Bring all the lighting equipment we have."
He glanced at Xiao Mai, who was curiously pawing at the entrance of the hole.
"And you, Xiao Mai," he transmitted his thought via [Beast Tongue]. "You're the most sensitive to things underground. This time, you'll be our scout. Notify me immediately if you sense anything wrong."
Xiao Mai meowed and was the first to dive into the dark tunnel.
The "Underground Exploration Team," consisting of Chen Shouzhou, A'Jie, and Xiao Mai (one cat), was thus formed. They cautiously entered the fire-scorched tunnel, following the direction of the lingering light towards the unknown darkness.
The deeper they went, the more humid the air became, mixed with the heavy smell of machine oil and rusted metal. At first, the tunnel walls were just ordinary dirt, but as they delved deeper, the surroundings began to change dramatically.
The walls gradually became smooth and flat, with large metal panels fixed with rivets appearing. The ground underfoot also changed from dirt to cold, hard concrete.
Chen Shouzhou shone his flashlight on the metal panels on the wall and touched them, exclaiming, "Holy crap! This isn't a natural rat tunnel! This... this is man-made! It's a ventilation duct or a sewage channel from a lab!"
"Chen-ge, look here!" A'Jie called out from a corner, where he had found a metal nameplate, half of which was corroded beyond recognition. He wiped away the grime and, by the light of the flashlight, could faintly make out a few blurry characters engraved on it.
"X7..."
At that moment, Su Wan'er, who was maintaining contact via walkie-talkie, also saw the number from the photo A'Jie sent back. Her face suddenly changed, as if she had remembered something extremely important. But she didn't say it immediately, merely noting down the location and number in her notebook.
They continued forward for about another fifteen minutes before the passage suddenly opened up. They had arrived in a huge hall, like an underground fortress.
The hall was in a mess, with scattered files and broken instruments everywhere. In the beam of their flashlights, they saw several long-decayed corpses in heavy protective suits, lying silently on the ground.
In the center of the hall, a huge, yellowed regional map hung on the wall.
Chen Shouzhou stepped forward, blew away the dust, and the contents of the map sent a jolt through his heart.
On the map, several "experimental sites" and "ecological monitoring zones" were clearly marked with red lines. And one of the coordinate points, marked as a "ground-level ecological observation station," after a quick calculation and comparison by Lin Mo, turned out to be... the exact location of their current safe house warehouse.
"Holy shit..." Chen Shouzhou felt a chill run down his spine. "You mean... we've been living on top of a massive old-era research base from the very beginning?"
This discovery answered all their previous questions. Why there were so many mutated creatures here, why there was so much abandoned equipment, why the system chose to activate here...
Just as he was overwhelmed with shock, the continuous "thump... click..." tapping sound abruptly stopped.
The entire underground hall fell into a dead silence.
Then, from the deepest part of the tunnel, came a low "humming" sound, like a surging electric current.
A faint blue light flickered in the darkness.
A small robot, about half a person's height and covered in a metal shell, its wheels making a soft rolling sound, slowly activated from the shadows and glided in front of them.
On the robot's mechanical arm, a line of red electronic text was flashing continuously.
"Welcome to X7 Ecological Monitoring Station... Verifying identity... Beep... Beep... Identity unrecognized. Classified as unknown intruder."
Chen Shouzhou was so scared his soul nearly flew out of his body. He immediately pulled A'Jie behind a massive load-bearing pillar, his heart pounding like a drum. He had a vague feeling that this seemingly accidental exploration might completely change the fate of their sanctuary.
However, the robot did not attack as they had expected. Its camera light flickered a few times, as if it were making some kind of judgment. Finally, its cold, mechanical voice echoed through the entire underground hall from a battered speaker.
"Warning: This facility is in an out-of-control state... Core energy system is nearing depletion... Without intervention from a human with the highest clearance, all cryogenically frozen A-class test subjects will be... automatically released... in 72 hours."
A harsh screech of static came from the robot's speaker, and a projection device on its chest cast a blurry video. The image showed countless huge, ice-coffin-like stasis pods, containing giant, terrifying creatures of unclear forms, submerged in liquid.
"...released..."
As the last word was spoken, the robot's power seemed to completely run out. The red light in its eyes slowly faded, the video screen went black, and the entire tunnel once again plunged into boundless darkness and silence.
Chen Shouzhou and A'Jie looked at each other in the dark, and they could see the shock and fear in each other's eyes.
A-class test subjects! 72 hours!
This was no longer a crisis. This was the Sword of Damocles hanging over their heads.
"We have to find out what else is hidden here," Chen Shouzhou said in a low voice, a tone of unshakeable determination in it.
They didn't dare to go any deeper. They immediately returned the way they came, carrying this earth-shattering secret with them.
And just after they left, the camera of the now-extinguished robot, in the darkness, quietly lit up again with a faint red glow, slowly turning in the direction they had left...