The seregant Major starts telling strange stories only after he drank 3 glasses of whisky. What can you infer from this information? Why didn't he start talking right away?

Normally people associate a "loose tongue" with the imbibing of any kind of alcohol. Obviously, the Sergeant Major had something on his mind, but he did not want to share something so dangerous unless he was a bit more relaxed. Once he has become warm and more comfortable, he is willing to tell the story of the Monkey's Paw and its terrifying background.