Seventeen-year-old Lena and her friends get stuck in the school dental lab, where an unlabelled paste and strange changes in the models turn a boring project into something unsettling.
Lena was already tired of this school year, and the biology project only made it worse. While everyone else complained about exams, she, Igor, and Marta had been handed the least glamorous assignment in the class: spend a week comparing different toothpastes on dental models and record the results.
The high school dental laboratory was usually just sterile light, minty air, and rows of white trays that looked as if they had been scrubbed into obedience. That night, though, the room felt wrong. Shadows from the frosted window stretched across the benches in crooked shapes, and the metal tools on the counter caught the light in quick, nervous flashes. In the middle of the table sat three plastic jaws, grinning back at them, and beside them a small glass vial filled with an unlabelled paste nobody seemed willing to claim.
"Are we even supposed to use that?" Marta asked, tapping the vial with one finger. The label wrapped around it was covered in Latin, the kind of thing teachers used when they wanted to sound more serious than they were.
Igor leaned over the table and gave a half-smile. "Probably some old sample they forgot to throw out. Unless the school is secretly running experiments on us."
Lena did not laugh. Something about the vial bothered her. The paste inside was too pale, almost luminous, and when she opened the first jaw model to start the test, the front teeth already looked faintly blue at the edges. She scrubbed once, then again, but the stain only spread, threading through the smooth plastic like ink in water.
"That’s not right," she muttered.
"You used too much toothpaste," Igor said, but his voice had lost its confidence.
Marta had gone still. She was staring at the microscope screen, her face drained of colour. Lena stepped closer and saw a close-up of something she could not make sense of: irritated, red tissue where there should have been only plastic and painted enamel, as if the model had turned inside out for a second and shown them something living beneath it.
The lights above them flickered once, twice, then steadied for a breath before dying completely.
In the dark, something clicked against the locked door.
Lena held her breath. The room was suddenly colder, and the mint smell thickened until it burned at the back of her throat. Then, from the table, came the faintest scrape of plastic against metal, and one of the molars on the nearest model shifted, just enough to make its grin look real.