Morse code

Alex glanced down at the watch. "Did you hear that? My classmate's gone missing in the Philosophy Hall. Could he have entered one of those spooky places?"

The watch ticked a few times, then a voice emerged: "There are so many strange places in this city. It's very possible that your friend has stumbled into one of them. There might not be monsters there, but there's definitely something weird. If there's an entrance to the place, your friend probably bumped into it. But I have to warn you, kid, in your present state, going in there is like delivering yourself as a meal."

Alex got up and collected his belongings. Although he hadn't known Tom for long, he couldn't stand by and watch an innocent person trapped in such a ghastly place. "Tom might be trapped. Now that I know some of the inside story, I can't just ignore it."

The watch snorted. "Alright, I can't stop you if you want to go. But take me with you. Maybe I can help."

Alex muttered, "What can you do?" His voice held doubt as he tapped the watch with his finger.

"Don't underestimate me!" The watch seemed unable to accept Alex's skepticism. Even the tip of the second hand trembled slightly as it moved. "I can save your life." After saying that, it fell silent.

Alex was silent for a moment, then muttered, "Alright." He slipped the watch into his pocket. He was thinking that if the tapping in the Philosophy Hall was really a portal to the Other Side, Tom's disappearance might not be an accident. But there didn't seem to be any missing person cases circulating at Columbia, so the Philosophy Hall should be a relatively safe existence.

His knowledge of the Philosophy Hall was limited to the strange tapping sound. There weren't enough clues, so everything would have to be improvised.

Alex sat on the edge of his dorm bed, packing his backpack. Again, he placed the watch in his pocket and patted it. It ticked, followed by a lazy hum: "Don't worry, I'm awake."

He zipped up his dark gray sweater, slung his backpack over his shoulder, and pushed open the door. Night had fallen, and only a few street lamps were lit in the campus, the Philosophy Hall lurking in the distance like a silent beast. He mounted his old bicycle, the tires rolling over the cobblestone path with a slight creak. The wind was a bit cool, and these blurred yet intertwined clues made a whirring sound.

The Philosophy Hall was located in the southeast corner of the Columbia University campus. A four-story red brick building, its outer walls were covered with ivy, and its narrow windows were like a row of contemplative eyes. Alex locked his bicycle to the nearby railing and looked up at the old building. The wooden entrance doors were closed, and the door frame was carved with elaborate patterns, the marks of time making it appear somewhat mottled. He tried to push it, but the door wouldn't budge. He went around to the side and found a window that was half open, the window frame was a bit loose, and ivy hung down like a natural screen. He took a deep breath, grabbed the windowsill, and climbed in.

When he landed, he was careful to avoid making too much noise. The interior was dim, the air filled with the scent of old books and wood. "I really have to bring a flashlight next time," he thought, then he turned on the flashlight on his phone, the beam sweeping across the hall. The interior of the Philosophy Hall was simple and dignified. The floor was dark oak, creaking slightly when stepped on, and the walls were hung with several oil paintings, the frames gilded, the figures in the paintings gazing intently, as if watching him. A long table sat in the center of the hall, surrounded by several high-backed chairs, the table top littered with several open books, as if they had been hastily abandoned. He approached and saw that the pages were yellowed, the title was "Metaphysical Inquiries", and there were several handwritten notes in the corner.

He looked up, his gaze falling on the stairs leading to the second floor. The banister was carved with complex vortexes, and a small statue stood at the top - a scholar holding a scroll, his expression solemn. Alex stepped onto the stairs, taking each step carefully, trying not to let the wooden boards creak. The thread mentioned that the tapping sound was on the fourth floor, so he had to find that wall first.

The hallway on the fourth floor of the Philosophy Hall was narrow and quiet, the walls were painted in light gray paint, slightly peeling to reveal the brick underneath. On both sides of the hallway were offices and classrooms, with nameplates hanging on the doors, mostly locked, with only a few emergency lights emitting a faint green glow. Alex remembered that the "Rituals and Taboos" class was in classroom 305 on the third floor, not far from here, about two floors away. He walked along the hallway, his eyes scanning each door, looking for the clues in the thread - "the wall on the fourth floor, the tapping sounds like Morse code."

He stopped in front of an inconspicuous wall, on which hung a faded bulletin board, with several yellowed class schedules and a handwritten "Please Do Not Disturb" note pinned to it. He tapped the wall, the sound dull, like an ordinary brick wall. He frowned, muttering, "Is it here?" The thread didn't describe the location specifically, only mentioning the fourth floor and the tapping sound. He wasn't sure if this wall was the right one. He took a few steps back, looked around, in the distance was a glass door leading to another hallway, and the shadow of the stairs was faintly visible behind the door.

He decided to walk around on this floor first and look for more clues. He continued along the hallway, past several locked offices, there was an old-fashioned water dispenser at the corner, the machine was rusty, and the sink was covered in a layer of dust. He pushed on a door labeled "Archives", but it was locked. He sighed, turned back, feeling a little annoyed.

Just as he was walking back near the "Rituals and Taboos" classroom on the third floor, a clear tapping sound broke the silence. Tap, tap-tap, tap - the sound was short and rhythmic, coming from not far away, like someone tapping on the wall with their knuckles. He stopped abruptly, his heart beating faster, and turned to look for the source. The sound wasn't loud, but it echoed particularly clearly in the empty hallway. He held his breath and said quietly, "It's coming..."

He followed the sound, his footsteps very light, afraid of disturbing something. The tapping was intermittent, with a strange regularity, as if transmitting information. He rounded a row of lockers and came to a classroom labeled "Seminar Room B", the sound coming from the wall next to it. This wall was separated from classroom 305 by a hallway, about ten meters away, and behind the wall seemed to be a storage room, the door labeled "No Trespassing", the lock rusty, obviously no one had opened it for a long time.

Alex pressed close to the wall, the tapping sound clearer: tap-tap, tap, tap-tap-tap. He squinted and muttered, "Morse code?" He pulled out his phone, opened a Morse code translator app, and tried to record the rhythm. Pieced together, it seemed to say "black, book," but it was incoherent, like an interrupted message.

"Black book? What does that mean?" He felt confused. The tapping stopped for a moment, then started again, repeating the same rhythm. His heart beat faster, his mind racing:

"Is Tom calling for help? Or something else?" He touched the wall, the wall was cold, vaguely exuding an inexplicable sense of oppression, as if something was watching from behind.

He pulled the watch out of his pocket and gently tapped the case: "Jason, did you hear that? What is it?" The watch ticked a few times, and Jason's lazy voice came: "This place is strange. The tapping might be a signal for an entrance, or it might be a trap. I have good ears, but that doesn't mean I know everything. If you want to try, go ahead, don't say I didn't warn you."

Alex was silent for a moment, feeling hesitant. He stared at the wall, the tapping still going on, as if urging him to respond. "If it's really Tom, I can't ignore it..." The image of Tom flashed through his mind, that quiet classmate who had asked him a question about ritual taboos in class today. He gritted his teeth and made up his mind. He pulled the hammer out of his backpack, holding it in his hand, the weight making him feel a little more secure. He muttered, "Jason, I'm going to try knocking back, listen carefully." The watch ticked and lazily responded, "Alright, you knock, I'll listen."

Alex took a deep breath, recalling the basics of Morse code. He decided to knock back a "who" first. He raised the hammer and carefully tapped on the wall, controlling the force of each blow to avoid making too much noise. Tap tap tap tap, tap tap tap, tap tap tap tap - after tapping, he held his breath, his ear close to the wall, waiting for a response.