Thanks for the Generous Reward of Only Math Homework

"Your movement just now wasn't that loud, was it?" Fatty lowered his voice, his expression strange. "Then why is the echo so clear this time?"

The echoes reverberating through the stairwell were even louder than Curly Hair's footsteps.

That defied the laws of physics!

And the rhythm of the echoes was off too; it didn't quite match Curly Hair's steps.

A horrifying suspicion arose in Fatty's mind.

With that thought, he slowly took two steps downward. His shuffling footsteps rang through the stairwell, and half a second later, he heard two thuds echo back.

"That's not right." Fatty's face turned green. "That doesn't sound like just the echo of our footsteps."

Though the number of sounds matched, neither the volume nor the timing did.

It wasn't just an echo. It sounded like someone was following them on the stairs.

Whenever they took a few steps, that person took a few as well. Because the sounds overlapped with the echoes, no one had noticed at first.

"Fuck, who's copying the way we walk?" Curly Hair looked up and down, but there was no fourth person in sight.

Fatty said, "Judging by the sound, they're not nearby. They should be some distance away."

Echoes came from both above and below, and they couldn't tell which direction the extra footsteps were coming from.

Summoning his courage, Fatty raised the lamp again and approached the gap in the middle of the staircase. He first looked upward. Above was still an endless stretch of stair railings; through the narrow gap alone, he couldn't tell whether anyone was up there.

After staring upward for a while and seeing nothing, Fatty lowered his head to look down.

The moment he looked down, he saw a deathly pale hand resting on the railing of the stairs below.

"Fuck!"