Pakistan's struggles with the Umpire Decision Review System continued on the second day at Trent Bridge, as they once again found themselves uncertain of how to use the technology to their advantage. After a wasteful first day, in which they had squandered both of their lifelines in the space of five minutes, their experience reached a new low when Azhar Ali declined to refer a caught-behind decision that, had he done so, would surely have enabled him to carry on with his innings.

The incident occurred in the 21st over, with Pakistan already close to meltdown on 41 for 3. James Anderson zipped a full-length outswinger through to the keeper, and belatedly joined the appeal as Matt Prior went up to claim the catch. Azhar's first instinct was to walk towards the non-striker, Umar Akmal, but seconds later he turned on his heel and walked to the dressing-room.

Subsequent replays, however, showed clearly that the ball had flicked Azhar's pocket on the way through to Prior, and there was no evidence on HotSpot that there had been any bat involved. Had the third umpire Marais Erasmus been presented with that evidence, in full view of the crowd via the replay screen, it is unlikely he would have upheld the onfield decision.

However, Pakistan's captain, Salman Butt, refused to blame his batsman for walking, and instead cast doubts about the reliability of the technology by stating that Azhar actually believed he had got an imperceptible edge on the ball.

"I think it was very honest of Azhar Ali, good sportsmanship," he said. "He edged it and he walked straight away. If we had taken the chance, who knows, it might have been not out because it didn't show anything and it also showed it clipped the trousers on the way. But he knew he was out, so there's no point taking the referral. If you are found out on the big screen, it doesn't look nice."

Butt recalled a similar incident during Pakistan's tour of Australia in January, when Michael Clarke survived a caught-behind appeal during his century at Hobart, when Snickometer picked up a noise as the ball flicked the sticker on the side of the bat, but the Hotspot replay proved inconclusive.

"Hawkeye is not 100 percent and neither is Hotspot," said Butt. "When the ball hits the sticker on the side [of the bat] it doesn't leave a mark. It happened with one or two decisions before. But the point is, if the batsman knows he has hit the ball there's no point taking a chance, because if it's up there on the big screen it's pretty embarrassing."

Either way, when coupled with the bloopers on the first day, most notably Kamran Akmal's crass decision to refer a catch that missed the bat by some distance, it's clear that Pakistan need some training in how to use the system to their advantage. England themselves had similar problems during the early stages of their tour of the Caribbean last March, but in recent months have become far more savvy.

"It's something to get used to," said Anderson. "We've not used it very well in the past and been on the wrong end of some tough decisions from it, but we've used it pretty well so far in this game. As it's used more and more in this game, the more we'll get used to it, and the better we'll use it.

"It's a case of knowing who to consult, because you've only got a short period of time to think before you refer," he added. "We try to keep as many people out of it as possible, and go for the three key people."