punkscully:

Sirius and Lupin had given Harry a set of excellent books entitled Practical Defensive Magic and its Use Against the Dark Arts, which had superb, moving color illustrations of all the counterjinxes and hexes it described. Harry flicked through the first volume eagerly; he could see it was going to be highly useful in his plans for the D.A.

this comes from my very staunch headcanon that remus broke sirius out of grimmauld place at least once