Curious case of the immovable bails

There is one easy way for the bowler to get the batsman out in a cricket match: hit the stumps.
However, that has not always been the case in this World Cup.
Five times in 13 games since the tournament started a bowler has hit the stumps and the electronic 'zing' bails have lit up but stayed firmly in place, according to BBC Sport.
Former England captain Michael Vaughan described it as "ridiculous" .
In the opening match of the tournament England leg-spinner Adil Rashid flicks the off stump of South Africa's Quinton de Kock with a delivery which goes to the boundary for four.
In the New Zealand and Sri Lanka match, Dimuth Karunaratne chops New Zealand pace bowler Trent Boult on to his stumps, hard enough to shake the bails but not dislodge them.
In the Australia vs West Indies match, Chris Gayle is given out caught behind off a 93mph delivery by Australia pace bowler Mitchell Starc, but the decision is overturned when TV replays show the ball hit his off stump rather than bat.
In the England vs Bangladesh match, Bangladesh's Mohammad Saifuddin miscues a pull off Ben Stokes on to his off stump. The bail lifts out of the groove briefly but does not fall.
In the Australia vs India match, Warner drags India's quickest bowler Bumrah on to leg stump via his boot. Again, the bail is not for budging.
Under the Laws of Cricket, a batsman is considered bowled if "a bail is completely removed from the top of the stumps, or a stump is struck out of the ground".
Law 29.1.2 adds: "The disturbance of a bail, whether temporary or not, shall not constitute its complete removal from the top of the stumps."
The zing bails have been in use since 2012, when they were approved by the International Cricket Council (ICC). They were used at the 2015 World Cup and have been regular fixtures in the Indian Premier League and Australia's Big Bash League.
The ICC said zing bails weigh more than standard bails but less than the heavy bails used in windy conditions.
TMS commentator Simon Mann said: "The stumps are rock solid and heavy. I held one in Bristol on Friday. Like trying to toss the caber."