what was fishy about the story of a trout in a glass case in a village side inn the author and one of his friend went to?

George and J. walk to Wallingford and enter a little riverside inn. They start chatting with an old fellow there. They look-upon a dusty old glass-case which has a trout in it. They talk about the trout's weight and admire it. The fellow says its weight is 18 pounds six ounces. He had caught it 16 years ago. Then he goes away. Then the local carrier comes. He claims that he had caught the trout nearly 5 years ago and it weighs 26 pounds. Once he goes, a third person comes in. He also claims he had caught the trout and so does a fourth person who says the trout weighs 34 pounds. He too goes away. Then the landlord comes in and he tells stories about the trout there. He claims he himself had caught the trout in glass case when he was a lad. This excites George and he climbs up the chair to have a close look at the trout. The chair slips and the case comes crashing. It turns out that the trout was made of Plaster of Paris.