The rain wiped out the neon sign "Oral Prevention Clinic" as if the night wanted to brush it down to the last droplet. Lena turned off the last treatment lamp and then quickly switched it back on - a habit taken over from practice: better to see the countertop before darkness fell. There was mint in the air after the rinse and something else, a shadow of eugenol, that old, comforting smell of the surgery that reminded her of her childhood spent in the waiting rooms at her grandmother Antoinette's. Her grandmother had left behind a silver mirror, old-fashioned, with a mint leaf engraved on the side and a tiny tusk instead of her initials. Lena carried it in her apron pocket, although she already had modern, lightweight tools and magnifying glasses with a lamp. This mirror was different. Sometimes, when she put it down on the tray at night, it seemed to reflect not so much her face as light from places where no ray would look - as if it had its own flash memory. That evening, the last patient, Natan, the barista from the café opposite, came in with hypersensitivity, air swishing through his teeth and apologising for his own enamel, as if it were a guest he had neglected. "I brush softly, twice a day, floss, rinse in the evening. No acids after ten o'clock. I promise," he recited. He had something of the barista in that rhythm as he refereed the profile of the beans. Lena lifted her lip softly in the lamplight. Dull islands glistened on the incisors and canines, symmetrically, like rain marks on glass. They did not look like typical neglect. They did not look at all like something she was used to. She took pictures, wrote down recommendations, reminded them of the break between an acidic drink and brushing, of a soft-bristled toothbrush with short strokes, of floss used without haste before bed. She didn't lecture - they both knew Natan was trying. When he left, he left a note on the counter with a cup drawn on it and the words: "For a smile that doesn't pinch". Tadeusz, a security guard with eyes like steel beads, pulled on his jacket. "Ms Leno, don't stay long. There's been something muttering in the basement for two nights. Like this... like a drill, only far away, as if in the walls." - he whispered, as if the ventilation could eavesdrop. "We've got the compressor off at twenty-two." - she replied, more to herself than to him. She knew the machines, knew the rhythm of the clinic better than her own breaths. A rhythm that was tangling today. When the surgeries quietened down, Lena turned on one more lamp and poured water from the unit tap into a disposable cup. Out of sheer curiosity: what does Natan hear, what do the pipes hear? Half-joking. She took out a silver mirror and dipped it into the water. The surface reflected the ceiling, the neon and her eyebrows, but then, for a brief streak, stave-like shapes undulated across it. Strands of sediment, speckles, light - everything formed for a moment into something that looked like notes. She blinked. The mint in the air seemed to intensify. She moved the mirror. The lines had arranged themselves differently - now they resembled the narrow streets of a map, with the main artery marked like a long cut of the mouth opening, connecting the front of the clinic to the back of the building. A drop of water fell from the rim of the cup onto the handle of the mirror and spilled out in an arrow shape, straight down - towards the basement. "Bullshit," she said in a half-hearted voice, as if evaporating her own thoughts. But she was already putting on her sweatshirt, grabbing her keys and a bunch of metal tags, hesitating a moment more at the door to the stairwell before she sailed down like a drop on the enamel. The basement corridor was narrow and cool. To the right hung old posters with eight golden rules: "Floss is the friend of interdental spaces", "Soft toothbrush, hard will". Cables scrolled between the pipes, a box with posters for schools and a box with packets of trial toothpaste stood in the corner. Tadeusz was already in the duty station. All Lena could hear were her own footsteps, the sound of rubber boots and... something else. A gentle buzzing, as if someone had turned the scaler on at minimum frequency and left it in the cupboard. The door to the technical room gave way reluctantly. Inside, it smelled of dampness, chlorinated water and dust, with a thin residue sticking underneath, like the back of a mirror after many polishes. In the middle - the filter system housing, no longer young. Someone had once carved a tiny mark on its metal plate: leaves and fangs, almost identical to those on Grandma Antoinette's mirror. "Coincidence!" - she spoke to herself again, only her voice sounded quieter now. She brought her hand closer, not touching any live parts. The indicator light pulsed softly, although the main switch was in the "0" position. This was not normal. Next to it, on the wire, a single droplet glinted - not water. Denser, like syrup. It didn't occur to her to check the taste; she had heard stories too many times about chemistry pretending to be something tame. She took out the pH strips, long ago left with the hygiene preparations. She swung a drop over the edge, letting it slide onto the strip. The colour hesitated and stopped at a shade that made her hiss quietly - too acidic for something that should pass through a filter system. She wiped her forehead with the willow of her hand. If it goes into the units, into the cups, into the mouth cavities.... Something clattered behind the wall. Not loudly, but clearly. Lena held her breath, looking at the metal ribs of the pipes. The clanking changed rhythm, as if someone in the adjoining room was adjusting the dial of the working fluids. She crouched down to look under the pipework, and then a silver mirror slipped out of her pocket. It rolled across the floor like a coin and stopped just short of the gap under a frosted glass door with the words in gold paint on it: "Instrument storage". She lifted it carefully. In its oval window she saw not her own fingers but a row of tiny porcelain keys. For a fraction of a second, she thought she could hear them pressing one at a time: the sound of the glaze singing with her breath. A micro-world scrolled across the surface of the mirror: tiny, luminous dusts were arranged in figures, as if someone had choreographed their dance. They had proportion and order, but not an order of purity - rather an intense poetry of adhesion. There was a logic in this poetry, a rhythm of repetition. "I hear you!" - she whispered, unsure to whom. And whether she should acknowledge it at all. She stood up and looked at the threshold. Someone - or maybe something - had passed through here recently. There were smudges in the dust of boot prints, washed out in narrow strips, as if someone had walked by dragging a ... hose across the floor? Or perhaps long, round suction cups? The smell of mint was more intense here, but not the drugstore kind, but fresh, as in the first hour after brushing. The skin on the nape of my neck tightened. The door handle refused to move. The lock was silent. Lena looked around and smiled in slight disbelief at herself. If she was going to teach the children at the Saturday school how to use thread, why not use a little cleverness? She pulled out a box of thread, unwound a long section and slipped it carefully under the door, aiming for the spark of metal on that side - as if a key would shine there. The thread entered the slot without resistance, moved patiently, millimetre by millimetre, up and sideways, until she felt a blunt resistance. She pulled gently, then harder. Something on the other side trembled. The buzzing of the filters became a complaint. The light on the housing blinked rapidly, like an eye before a tear. Then, instead of the expected flutter against the key, came a different feeling. The tension of the thread. As if someone had grabbed the end of it on that side and clamped it between their teeth. One tug, another. The thread tightened to its limits. The silver mirror in her hand became warm, as if it had suddenly caught a fresh light. Lena pressed her eye against the frosted glass of the door, trying to see anything. A soft, clear sound came from inside - like the first touch of a scalpel against a porcelain cup. And then someone, on the other side, began slowly pulling the thread inside.