The Common Room was silent for ten seconds.
Only the charcoal crackled now and then.
Harry had not said a word.
He was looking at the three-dimensional breakdown diagram on his knees.
The left half of the sheet showed a human outline.
Dense clusters of numbers and arrows marked the figure's head, torso, and limbs.
The right half was a series of formulas.
"I've been thinking about something."
He spoke.
Ron and Hermione both looked at him.
"The professor wrote a passage in the Fifth Year booklet. About how fast humans process visual information."
He turned the sheet over.
"Normally, the eyes pick up an object's trajectory, the signal travels to the brain's visual cortex, the brain analyzes its speed, direction, and threat level, then sends instructions to the motor nerves, and the arm starts moving."
"How long does that take?"
He answered his own question.
"Zero point two to zero point four seconds."
"But the Reductor Curse's flight time is zero point three seconds."
He looked at Hermione.
"At a distance of five meters, from casting to impact, zero point three seconds. If I follow the normal sequence-see, analyze, decide, act-the spell will already have reached me by the time my arm starts moving."
Ron opened his mouth, then closed it again.
"So I need to skip the step in the middle."
Harry traced a line on the diagram with his finger, connecting "visual detection" directly to "motor command," bypassing "brain analysis" in between.
"Vision picks up an expanding point of light. The signal bypasses the brain's analytical regions and sends instructions straight to the arm."
"Without identifying the spell."
"Without calculating the angle or force."
"Without making any conscious choice."
"See light-block."
"See light-Deflect."
"See light-dodge."
He put down the diagram.
"I need to be an activated missile