From The Times :
A second highly contentious ruling in successive days by Darryl Harper, the third umpire, may yet prove a pivotal moment in this third Test.
If Harper’s decision not to call a no-ball when Alastair Cook was leg before on the first day was one of those 50-50 cases that England eventually chose to accept, the Australian official’s failure to pick up the noise of an edge from Graeme Smith appeared to have been a bad error on his part.
Cutting at Ryan Sidebottom early in the morning session when 15, Smith was reprieved by umpire Tony Hill despite impassioned appeals from England close fielders, who clearly heard something. The South Africa captain added a further 90 runs to his score before England eventually dismissed him, Andrew Strauss taking a smart catch at first slip after Smith edged a ball that left him in the air - but the damage had been done.
The decision to give Smith not out had immediately been referred to Harper, who rejected the review. When the television tapes were played back, a noise was clearly audible, although no deviation could be seen either by Hawk-Eye or the naked eye. Often, a very thin edge, or ‘feather’ as it is known in the game, cannot be picked up on TV, but the noise could not have been anything bar an edge as the bat was a long way from the pad and ground.