Lupin smiled wryly.
¡°Mr. Malfoy has just been to see me with a strange story, Potter,¡± said Snape.
¡°But he didn't even break his glasses.¡±
¡°This is a useful little spell,¡± he told the class over his shoulder. ¡°Please watch closely.¡±
Lupin was struggling against his bonds. Black bent down quickly and untied him. Lupin straightened up, rubbing his arms where the ropes had cut into them.