He was on his way out of the building, heading from the training hall to the lifts, when he spotted Potter at the end of the corridor, and he unintentionally froze (fortunately, the witch behind him had fast reflexes and had managed to avoid careening directly into his back). Conscious of the foot-traffic behind him, Draco unstuck the soles of his feet enough to melt back against the wall and out of the middle of the corridor.