Some Celtics may still wonder just what, exactly, is the desired carryover effect from embarrassment. After losing by 26 points in Charlotte on Tuesday for their second stumble of the season in the Queen City, they opened last night on uncertain legs. Kevin Garnett, out with what was described as a strained adductor in his lower left leg, was filling the Paul Pierce role. The Celtics captain missed Tuesday’s misery for strictly rest purposes. Thankfully for the Celtics, their adrenaline finally released on time to match their need for revenge in the second half of last night’s 105-88 win over the Bobcats. Defense, per usual, was their trigger, with the result a pair of huge second-half runs — a 16-4 spurt that consumed the middle chunk of the third quarter, and a 15-3 burst that carried from the late third into the early fourth. Those two sequences restored faith so convincingly, no one could remember the low energy that preceded it.