Lena worked at night in the Museum of Smiles, hidden above an old dental clinic on the market square. She carried her own kit in her backpack: a sonic toothbrush, floss, a soft tongue scraper and a small liquid. The routine of two minutes, circular motions and flossing after dinner calmed her better than the radio. Tomorrow she had a routine check-up with the dentist, so she put the sweets away and sipped only water. That evening, however, the minty smell in the halls was too intense, as if someone had been flushing the walls. What she liked best was the giant molar with the passage in the middle and the shiny, century-old mirror from her grandmother. Dr Sophie Wierzba donated it to the museum, saying that everything reflects better when the enamel is clean. As Lena walked past, the panel fogged up from the inside and a sentence was written on it. Floss before I penetrate - the letters flowed like sediment, leaving a sweetish dust on her finger. Lena shone the torch from her phone and saw a map of the city in the mirror, drawn with the film of the raid. The river glittered like thread, bridges looked like threadbare arches, and dark spots swelled like uncleaned pockets. A soft buzzing sound came from deep in the room, rhythmic like a toothbrush with a two-minute timer on. At the same moment, a molar trembled and slid a tiny service door out of the side. Closed with something like interdental brushes, the door flashed red and the quiet scraping of stone came from inside. Rules and regulations forbade opening the installation, but the mirror recorded the words again, this time with a drip like wash. Enter only with a clean heart and a clean glaze - and then it hissed like freshly poured liquid. Lena threaded her way through the grate, hooked the tiny key and slowly pulled it towards her. For courage, she measured out a portion of the liquid, rinsed her mouth for thirty seconds and spat it into the service beaker. Previously invisible marks appeared on the surface, folding into a line like brushing instructions. Accordingly, Lena moved the key, heard a click and felt a warm, sweet blast from inside. A chorus of whispers sounded outside the threshold repeating the rhythm: twice a day, two minutes each, no rush. Lena tightened her hand on the toothbrush, pressed the button with a soft beep and took the first step into the darkness. The corridor was as smooth as glaze, but tiny cilia pulsed at the edges, resembling spilled sugar. Fluoride crystals glittered on the ceiling, and in the distance someone in the shadows moved very quietly. - 'Give back the toothbrush, Lena,' whispered the echo in her grandmother's voice, only stickier and stranger. From her coat pocket rang the minute hourglass she carried on duty, although she never used it. A silhouette emerged in front of her with a smile too white, without contours, with a gap like a black gate. The air thickened, the toothbrush vibrated harder, and a hand with an invisible tarnish stretched towards her from the darkness.