What is the first hint that the monkey’s paw is not a good thing?

The first hint that the monkey's paw is not a good thing can be seen in the Sergeant-Major's response to Mr. White's question. When Mr. White asks why his friend hasn't had his three wishes..... the Sergeant-Major's voice changes, and he pales.

The soldier regarded him in the way that middle age is wont to regard presumptuous youth. "I have," he said, quietly, and his blotchy face whitened.