Mirror Twin Dash

Two runners. One finger. They refuse to move the same way. Drag upward and the top runner climbs while the bottom one sinks. Drag down and they swap. Somewhere ahead, a pair of gates waits at mirror heights, and both runners have to pass through at the same time. It is a small, absurd kind of coordination: your hand does one thing, your brain tracks two bodies. Miss the gap by a hair and the pair stumbles. Find the offset and they slip through like they planned it all along. Ten seconds to learn, a hundred runs to master.