Midafternoon, and Snape was alone in his makeshift lab, when he felt an entirely new sensation. A twinging, stabbing ache, precise but also weirdly distant, as if someone had started first to poke and then to stab at one of his toes with needles dipped in acid: if his body was so huge that his extremities could be miles away. The sense of painful intrusion was that precise, that personal. Coming from that direction, that distance.
The tunnel! FUCK!
He didn't even pause to banish the phial he was holding back to its rack; it fell forgotten from his hand to smash on the flagstones as he lifted off. As he flew from his quarters in a blur of speed, he sent firewriting messages to Moody and Potter: Post office tunnel discovered, wards under attack: still intact for now. Reinforcing, but can't hold forever. Meet in planning room. The rest of his attention was focused on blasting doors open in front of him quickly enough that he didn't crash headlong into them, in the furious rush of his flight.