spike discovers that the chip in his head gives him no pain when he punches buffy. after verifying, with warren's help, that the chip appears undamaged and still causes him agony when he harms humans, spike tells buffy that she "came back wrong" and that she "has a little demon" in her. in furious disbelief, buffy assaults spike and they battle until buffy unleashes her desire and kisses him, initiating such passionate sex that the abandoned house in which they were fighting collapses around them.