Iruka lifts his hand and lets silence take its place.
"On my word," he says, tone thin and patient. "You will cause an error and catch it in the same breath."
He lowers his hand. The room becomes a listening thing.
"Demo one," Iruka says. He walks to a front desk and nudges a pencil until it hangs half over the edge - not falling, only thinking about it. He does not look at Izayoi when he says, "Receive."
Izayoi steps forward with palms visible. He does not snatch. He lets the pencil meet the inside ledge of his fingers because his fingers were already where gravity planned to be. The pencil never becomes an event.
Iruka nods. "Dodge makes noise. Receive makes less. Class - pairs. Choose one pencil. One partner knocks it wrong. The other receives. You will not chase it. You will not do a show. You will make nothing for the floor to remember."
Pencils tap to desk edges throughout the room. Small hands misjudge distances by honest millimeters and then start learning what millimeters are for. Hinata lifts a pencil to the same half-over line, breathes, and lets it go. Izayoi receives without a sound that would call attention to itself. They switch. Izayoi sets it half over; Hinata meets it with the softest part of her fingers like a door that opens because a house has good habits.
"Three words," Iruka says as chalk note. "Speak as you work. No sentences."
Hinata: "Angle. Breath. End."Izayoi: "Less. Quiet. Close."
Naruto knocks his pencil too hard and it hops like a fish. He panic-catches with a clap and almost sends it farther. Shikadai turns the clap into a bowl by adding his palm underneath. The pencil accepts the second chance without complaint.
"Words," Shikadai murmurs. "Plan. Small. Hands.""Right," Naruto says, half to the pencil and half to himself.
"Demo two," Iruka says. He drags a satchel strap into the left aisle and looks at it the way a person looks at a puddle they will walk through on purpose. "Strap trap. Step onto wrong - save with ribs only. Ankles home. Palms up. If your foot scrapes, pay five."
Izayoi comes to the line. He lifts his palms higher, lets everyone see what he is not about to do with his hands, and sets his heel where the strap wants to roll. It does. He lets ribs carry the small changing angle. Ankles stay where they belong. The strap thinks it made someone else kneel and then does not get paid.
"Again," Iruka says. "Other foot."
He does it with the other foot and saves it sooner - not faster, sooner - because practice makes the catch arrive where physics would rather be lazy than proud.
"Mirror," Iruka says to Hinata.
Hinata steps to the strap like it has a rank and she understands it. Palms up. Heel wrong on purpose. The leather tries to roll her ankle and finds the ribs under orders. She keeps her shoulders quiet. The room hears nothing.
"Three words," Iruka says.
Hinata: "Choose. Before. Place."Izayoi: "Ribs. Pay. Less."
"Pairs - your turn," Iruka orders. "One straps. One steps. Switch. If you scrape, pay five."
The aisle fills with straps - too far out, not far enough - and the sound of leather learning its own job. Three students scrape. They pay quickly. Naruto almost scrapes and then remembers ribs exist and does not.
Iruka is already at the back row by the time the last pair steps. "Demo three," he says, and puts two fingers on a chair back. The chair slides two inches into the narrow part of the aisle - the kind of wrong that ruins tempers if you think the world owes you space.
"Near bump," he says. "Solution is not a trick. Solution is a stop."
Izayoi arrives, sees, and does the small hardest thing: he stops. Not with a flinch - with a decision. Palms still up. Feet still home. The chair owns the inch. Izayoi does not turn a furniture mistake into a person mistake. Then he starts again.
Iruka taps the chair with the back of his knuckles. "Cheap pause," he says. "Cheaper than collision. Cheaper than apology. Practice stopping. Class - you will each build one stop."
The room learns there is a way to stop that does not shout. Hinata makes her stop as if she had already planned for it and only had to remember where in the plan the pause lives. Naruto overdoes his first stop by planting both feet like a tree discovering pride. Shikadai says, "Smaller," and Naruto finds the inch he can afford.
"Good," Iruka says. "Now we stack. Pencil - strap - chair. Cause three wrongs, catch three wrongs, no noise, no story. Go."
Pairs begin the circuit. Pencils knock, receive. Straps roll, ribs pay less. Chairs intrude, pauses appear. The air fills with small decisions that never ask for applause.
At the far right lane, a boy insists on dodging the strap with his knee and reaps a desk corner on his thigh. The thud is dull and honest. He winces and keeps his mouth closed by choice. Iruka points with two fingers. "Five. Pay. Then say your three words before you move again."
The boy drops, pays, and says, "My - fault - smaller." He means all three.
Hinata sets her pencil wrong and receives it with the pad of her palm. She sets the strap wrong and saves it with ribs. She steps into Izayoi's lane at the chair and pauses - a stop so measured it feels like a bow to the room. They switch without speaking. Izayoi runs the same trilogy with exactly the amount of attention it deserves - no more, no less.
"Words," Iruka reminds.
Hinata: "Hands. Ribs. Stop."Izayoi: "Choose. Before. Return."
Naruto tries the trilogy like a climbing problem. Pencil first - he improves, hands a bowl now instead of a clap. Strap second - he nearly sings the word "ribs" out loud and thinks better of it at the last syllable. Chair third - he halts only one foot and nearly tips. Shikadai reaches a single finger and steadies him at the elbow without making it a rescue.
"Three words," Shikadai says."Almost - loud - quiet," Naruto says, and grins because the order matters.
Iruka walks the central aisle and listens to language turning into posture. He stops by the board, draws a tiny rectangle of chalk on the floor beside the small square already there, and labels neither.
"Pairs - new rule," he says. "Build an error that involves a person. Not collision. Not heroics. A near bump - a near step on a heel - a near reach past a face. Catch it clean. If words leave your mouth that are not necessary, pay five."
There is a new quality of careful in the room as people begin to risk social mistakes on purpose. A girl reaches past her partner's cheek for the pencil that does not need to be reached for. She slows and stops her own hand a finger width before privacy becomes a tax. She retracts without shame. Both nod because the lesson already happened.
Hinata and Izayoi face each other inside a polite rectangle of space. Hinata drifts one shoulder into the path his step wants and then holds instead of flinching away. Izayoi chooses the stop again - the smallest one - then continues as if the plan always included that inch.
"Good," Iruka says, and it means for the whole room.
He looks across the class to find the places where mistakes are about to get expensive and arrives there first with his attention. He never raises his voice. The room raises its own expectations.
"Three words - last set," he says. "Then we will make a door."
Hinata: "Near. Stop. Continue."Izayoi: "Price. Cheap. Paid."Naruto: "Almost - sorry - fixed."Shikadai: "Pause. Before. Pride."
Iruka kneels, draws a tiny door beside the chalk square and rectangle, and gives it a thin outline with the care of someone who understands stagecraft. He stands and puts the chalk back on the rail. He does not label the door. He looks at it and the class looks because he looks.
"Next module," he says. "The Thin Door. The room is about to pretend to be a street. Doorways are where people lie to themselves about space and time. You will traverse the door - one at a time - with the same small rules you used in the corridor. Palms visible. Ankles honest. Ribs before shoulders. Stopping is cheap. If the door wants to teach you a lesson, you will pay the cheap one by choice."
He points at the actual classroom doorway. In the hall beyond, the day waits with the attention span of dust.
"Order," Iruka says. "Row by row. Naruto - you are not first and you are not last. Hinata - second in the first row. Izayoi - anchor the first pass. Mizuki will observe from the frame and will not speak."
The frame already holds a quiet man in a flak vest who has learned how to be furniture. Mizuki inclines his head without stepping into owning the room. Clipboard remains at rest.
Iruka looks at the tiny chalk door again, then at the real one. He lifts one finger.
"On my count," he says. "The door will insist on being narrow. You will make yourself smaller instead of louder. If you need to stop, you will stop, and the person behind you will pay by waiting and not by pushing."
He raises a second finger.
Pencils fall still. Chairs learn to be quiet. Ankles remember home.
Iruka moves the third finger up and lets the room feel the hinge about to turn.