Inflexibility

A man rings the pet shop, and asks for a dog.
"I've got a live cat and I've got a dead dog,"
Said the owner, "Which one will you have?" 
"I want a dog, a dog I must have,"
Said the man, "Of cats, I'm no fan."

The owner brings the dog around in his van,
Takes payment, and makes off as fast as he can.
They find that the dog will not play with the kids,
As you'd hope that a household pet should;
But - there was no reason to expect that it would.