POTTER-!" he roared making Draco flinch in alarm, but Harry was quick to respond, silencing the man almost instantly. He bared his teeth, and countered Harry’s spell with just as much speed. Harry frowned at him and silenced him again. On and on they went, until they must have spent a good two minutes silencing and unsilencing while Draco watched them looking increasingly bewildered. When a bead of sweat began to gather at the Professor’s brow, Harry knew he was beginning the drain: wandless magic was tiring, no matter how small the spell.