Sheila loved her two dogs, but they were very disobedient, so she decided to take them to obedience classes.

The class was run by an old man. He was very strict but seemed to get good results, and after several months of regular attendance things had improved to such a degree that Sheila was even considering entering her pets into a dog show.

But then one day, disaster struck. Sheila had to baby-sit for her young nephew. All evening, the boy teased the dogs, and by the end of the day both dogs were back to their old habits - all the hard work and training was undone in a single evening; it was as if they had never been to class at all.

Worst of all, it was only a few weeks before the dog show, and she had already registered her entry. What could she do?

In desperation, Sheila decided to call a friend of hers who also had two dogs of the same type that did behave themselves, and asked to borrow them. Her friend agreed, and at the next class Sheila arrived as usual with two well-behaved dogs.

But the old man wasn't fooled for a moment - as soon as he saw them he knew they were the wrong dogs, so he called Sheila over to the side of the class.

"It was a good try," he said, once he'd heard the story, "but you should have realised that you can't trick an old teach with new dogs."