This 2D companion to the 3D rain-window simulation looks straight at a pane of glass from indoors: raindrops land and grow into round beads held in place by surface tension and adhesion, until a droplet's weight along the tilted pane finally overcomes that pinning force and it slides, coalescing with every droplet in its path and leaving a streaked trail behind it. Raise the rain intensity to flood the glass faster, and tilt the pane toward vertical to watch smaller and smaller droplets break free and race down — the same contact-angle physics that decides whether a raindrop clings to your car window or streaks straight down it.