Mystery behind an egg inside an egg

A woman was left shell-shocked when she cracked open an egg only to find another one perfectly intact inside. Smallholder Chris Keast, 60 thought his wife Jane, 55 was cracking up when she made the amazing discovery while preparing their tea. The Cornwall couple couldn't believe their eyes when she broke the extra-large egg and the second one simply rolled out into her frying pan.
When she told husband Chris he thought she was joking but ended up reaching for his mobile phone to take a picture when he looked at the pan. The inner-egg was the size of a 2p piece and its shell was still in one piece. Jane cracked it open and found there was no yolk inside, just the egg white. Experts say the rare phenomenon is just a quirk of nature and can occur if the hen receives a shock during egg production.