What effect does him striking a few chords on the piano have on this scene? *The monkeys paw is the story*

The paragraph - His father, smiling shamefacedly at his own credulity, held up the talisman, as his son, with a solemn face, somewhat marred by a wink at his mother, sat down at the piano and struck a few impressive chords.
"I wish for two hundred pounds," said the old man distinctly.
A fine crash from the piano greeted the words, interrupted by a shuddering cry from the old man. His wife and son ran toward him.
"It moved," he cried, with a glance of disgust at the object as it lay on the floor.
"As I wished, it twisted in my hand like a snake."
"Well, I don't see the money," said his son as he picked it up and placed it on the table, "and I bet I never shall."
"It must have been your fancy, father," said his wife, regarding him anxiously.
He shook his head. "Never mind, though; there's no harm done, but it gave me a shock all the same."