The Married Couple

There once was a Welsh couple who had been married some years before the husband realised that his wife kept a box under their bed, and wore the key for it around her neck. Curious, naturally enough, he demanded to know what was in the box, but of course she would not tell him. 'I'll let you know on our golden wedding anniversary,' she promised.
The years passed but despite the husband's occasional attempts to find out about the box, the wife remained adamant. Not till their golden wedding would she divulge the secret of the box. Well, of course, the anniversary arrived and their children gave the couple a great party. It was well and truly early morning before husband and wife made their way up to bed. 'Uh-ho,' said the wife, 'I am so tired. I think I will go straight to bed.'
'No, you don't,' said the husband. 'We have an arrangement. Tonight was our golden wedding anniversary, and you have promised for years to show me what is in that box under the bed.'
'Very well,' said the wife, taking the key from her neck and unlocking the box. Inside were three eggs and about £5,000 in cash.
'What does this mean? What are those eggs doing in the box?' the husband demanded.
The wife sighed. 'You won't like this. But you insisted on knowing. Every time I was unfaithful to you, I put an egg in that box.'
The husband was devastated and furiously angry. He roared and he thundered. But after a while, he said, 'Well, it's only three eggs, after all. I forgive you.' And he kissed her, and then she locked the box and put it back under the bed.
Only then did it occur to the husband to ask about the money. 'What's that £5,000 doing in there?' he said.
She gave another sigh. 'It's like this,' she said. 'Whenever I accumulated a dozen eggs, I sold them for £1 ...!'