"Avada Kedavra"  the green light flashes from his wand points and the rat is stunned for a moment and continues its useless search.  He casts it again and again, exhausting all his magical energy and a sheen of sweat breaks out above his brow. The spell chips away at the floor and even takes out a bar on a cell but the rat continues to survive. Finally, on his seventh try, anger bubbling over in his veins he screams and casts it one last time.