Dr Mint's office shone like a new coin. A neon tooth shimmered on the glass, the inside smelled of eucalyptus and mint, and colourful posters hung on the walls: "Brush twice a day", "Floss like a ninja between your teeth", "Fluoride strengthens enamel". Two white pinwheels spun from the ceiling, whispering quietly as if watching over every speck of toothpaste. It was Saturday and the Open Smiles Night was taking place. Zosia and her little brother Olek slept in sleeping bags between the dentist's chair and a shelf with woven baskets for dental floss. On the table next to them stood a blue hourglass measuring two minutes, brushes in cups lined up in a row like colourful soldiers, and glitter mirrors for the children lay next to a model of a giant tooth. - 'Welcome, smile researchers,' said Dr Mint, correcting her green-leafed cap. - Today you will learn toothbrush manoeuvres and tricks with a floss. And if you are very attentive, you will see something that sometimes escapes the naked eye. Zosia felt her heart do a 'hop'. She loved words that sounded like a promise of adventure. Olek looked around the office with the look of an amusement park caving. He moved the backpack with the comic books under the radiator and immediately started rummaging in the drawer marked "Models and aids". - Just be careful! - exclaimed the doctor, smiling. - The whole history of teeth lives in this drawer. Strange treasures glittered inside: an old metal mirror case, a large pair of tweezers, a porcelain smile and a neat box marked 'Flash 7'. Olek pulled out the last one and opened it. Inside lay a thin thread that looked like a silver spider web coiled in a circle. - What's this? - he whispered. - 'It's a special show thread,' replied the doctor. - We don't use it every day anymore, but it has one interesting property. When it gets close to places that need to be cleaned, it sometimes... buzzes. - Buzzes? - repeated Olek, immediately pressing the disc against a large model tooth. Nothing happened, but Zosia noticed that there was a buzz right at the neck of the model, as if a wave of quiet whispering had passed from there. After the official part, the children arranged their sleeping bags, while Dr Mint poured warm water into their cups and showed off their new toothbrushes. - 'Remember: soft bristles, sweeping movements from the gums, two minutes,' she said. - And where the toothbrush can't reach, a floss will help. Gently, without tugging. Why? Because gums like to be handled like friends. - And bacteria don't like to have their lunch taken away from them," added Olek with seriousness. - Sugar. - That's exactly right - nodded the doctor. - They form a sticky film, we call it plaque. We fight it every day before it becomes hard as stone. And now... good night. I'll be in the office next door. If there's anything, call out. The lights dimmed. The neon tooth on the window pulsed like a silent lantern. Zosia lay for a moment with her eyes open, listening to the murmurs of the cabinet. The teeth in the display case gleamed, as if winking at her in communication. The hourglass turned itself over with a quiet click, as if to remind her that time passes even at night. - Are you asleep? - hissed Olek. - Almost - whispered Zosia. - What are you up to? - This thread. I want to see if it really buzzes. Zosia sat down and took a torch out of her backpack. The narrow beam spilled milky light across the large molar model. Glitter glittered in the recesses of the enamel, and the plastic tongue on the stand looked too realistic not to wave it. - Just be quick,' muttered Zosia. - 'I don't want the doctor to think that we're rocking the surgery. Olek brought the thread closer to the gap between the two white blocks of the model. At first, nothing. And then Zosia heard it clearly: a quiet "bzz-z", as if someone had touched a thin guitar string with their finger. The string twitched. The tooth model trembled so slightly that it might have seemed like just a draft. But there was no draught in the surgery. - See? - whispered Olek. - She's alive! - She's not alive. She's reacting - Zosia corrected him. - Reacting to what? Three pale circles of light moved from the torch. One fell on the sink drain. Something in the depths flashed like a sugar crystal. The second stopped on a poster with flossing instructions, the third right on a large model of a molar. Zosia squinted her eyes. A speck, like a speck of sparkle, slipped through the striated valley on the surface of the model. She rubbed her eyelid. There were more tiny particles. They were arranged in a kind of bridge. - Plate lights," muttered Olek, delighted. - I came up with the name. - It sounds good - Zosia admitted, but her voice trembled slightly. - Can you smell it? The air became sticky-sweet, as if someone had inadvertently sprinkled icing sugar and added a drop of raspberry syrup. The hourglass clicked again: two minutes passed, though no one turned it over. The sink clattered quietly. Zosia glanced at the 'Models and aids' drawer, which slowly, almost imperceptibly, slid out on its own. - Hello? - called out Olek in a half-hearted voice. - Doctor? Only a distant tapping answered from the next room, as if someone was arranging metal instruments in even rows. - Let's go on - Zosia decided, feeling that pleasant tickle of curiosity that always won out over reason in her. - Take the toothbrush. They took one each. Zosia grabbed her new green one with soft bristles. Olek selected a blue one, and wrapped the silver thread carefully around his fingers, as the doctor had taught. First they put the brushes against the surface of the model and began to move them as they had practised before - sweeping, slowly. The glitter on the tooth rippled, and something that looked like a miniature bridge splashed into a shimmering cloud. The thread sounded, louder this time, like a small bell by a bicycle. - See? - triumphed Olek. - We are working! - It's just a model - reassured Zosia. - It's just a... Suddenly she remembered a tiny box with the inscription "Flash 7". She looked at the letter 'ł', which flashed like a torch beam. And then she saw something else. A crevice, as thin as a crack in the ice, had opened up right at the root of the model. A chill and herbal air blew from inside. It smelled of mint. And something sweet. - Zosia... - Olek froze, as if someone had pressed pause. - It's opening up. Zosia knelt down. She put her ear to the model. She heard a sound like a street murmur from very far away: thumping, clattering, clattering, the laughter of someone very, very small. She felt a draft on her cheek. When she moved her toothbrush, the crack twitched, as if waiting for the right movement. She tried as the doctor had shown - from the gum upwards, gently but firmly. The fissure flashed with a brightness that did not look like ordinary light. Rather like a flash in a streak of paste, gliding through drops of water. Zosia withdrew her hand as the brush hairs rustled like grass in the wind. The thread in Olek's fingers began to pulsate, and the end of it slid out towards the clearance, as if he could feel an invisible draught. - 'It's like a door,' said Olek, in a hushed voice. - A door to... - 'Don't say that,' Zosia interrupted him, recalling the posters and all the serious looks on Dr Mint's face. - If it's some kind of... entrance... then maybe we shouldn't go in there. - But if someone needs help? - muttered Olek and pointed at the moving pollen, which at that moment formed into letters, just like mist on the glass. Zosia rubbed her eyes. It couldn't be real, and yet she read: "Too much sugar. Defend the glaze." The letters splashed out at once, as if someone had blown them. Zosia looked at her reflection in the study mirror. She was pale, but there was the same gleam in her eyes that appeared when she found a new book to absorb. She turned the hourglass over. The sand began to fall slowly, in an even stream. Like a countdown. - 'Okay,' she said, more to herself than to her brother. - We put the toothbrushes in. Just the tips. And we don't touch anything with our hands. - And we don't swallow the toothpaste," added Olek, as if that mattered at the luminous door in the tooth model. When the bristles touched the clearance, everything happened very quickly. The sink clattered louder than before. The neon tooth on the window shone like a firework and dimmed again. A soft, steady clatter could be heard in the study, as if someone was walking up the stairs with thin spoons. The air thickened with the fresh scent of mint, and sugar sparks danced in a swirling circle. The thread in Olek's hands shot out in a thin beam and clung to the edge of the crack like a seatbelt. Zosia felt the floor tremble - not like with the truck outside the window, but like with a tiny but persistent shaking that starts in her toes and goes all the way to her knees. The world around her has become... bigger. The plastic ruler on the coffee table had grown to the size of a bridge, and the toothbrush cup looked like a tower. - Zosia... - Olek grabbed her sleeve. - Either the study is growing or we are.... He didn't finish. From the clearance, which was now as wide as a garage door, came their distinct, audible sound. Something between a quiet 'crunch' and the clatter of glass balls. And then a rippling cloud of white particles came from within, shaping themselves into sharp, glittering needles with each blast. - 'They're crystallising,' Zosia whispered, feeling her heart pounding in her throat. - It's the sugar. At the edge of the light a shape blurred. First just a shadow with a rim of glittering crystals, then the outline of something that had many tiny, tapping feet. The thread rang quietly, like a warning. The hourglass had reached the end. The sand stood still. A whisper came from the clearance that sounded like the giggle of spilling sugar: - Who dared to move my building? Zosia lifted her toothbrush and Olek tightened his fingers on the thread. The shape made of crystals moved and headed towards them, faster than they had time to take a breath