The expression signifies an event that is highly improbable or virtually impossible. An example of its usage is to dismiss a suggestion as unrealistic, akin to expecting swine to take to the skies. The addition of a nighttime salutation serves to further amplify the unlikelihood and finality of the stated condition.
The underlying benefit of employing such a phrase lies in its ability to succinctly convey skepticism or disbelief in a colorful and memorable manner. This idiom draws upon the inherent absurdity of the image it evokes, making it easily understood across various demographics. Its origins likely stem from observations of the natural world and the limitations of certain creatures, contrasting those limitations with the realm of fantasy.