Krul has delivered the promise he showed as a teenager when Newcastle took him from Holland into their academy.
He told the Daily Mail: "I had the pleasure of training with Shay and Harps every day and then Pavel Srnicek came back and he trained better than us at 38. He was a training animal.
"I made my debut far earlier than I expected, then the club told me to go out on loan. That was really what made me a better goalkeeper.
"At Carlisle, we trained at the stadium, cold showers, pay for your own lunch, it was incredible. It is like man football. You need to experience those things because you are spoiled at Newcastle.
"I remember when I was at Falkirk over the Christmas period and we had three games in one week. In the first game I made a mistake during the first half and at half-time one of the senior players said, 'Listen, it's Christmas and I need the win bonuses to pay for my kids' Christmas presents so don't even think about making a mistake like that again'."
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