Something with short-lived popularity. The idea is that a song, a fad, or anything else that captures the public's fancy starts out like a house on fire but begins to pall after a little more than a week. The proverb “A wonder lasts nine days, and then the puppy's eyes are open” refers to dogs being born with their eyes shut; like them, the public is blind to the fad until they become sated or bored or both and then their eyes metaphorically open. The earliest recorded use of the phrase came from William Kemp, an Elizabethan comic actor, who in 1600 did a Morris dance over the 130 miles from London to Norwich. His account of his nine-day dance-athon was titled Kemp's Nine Daies Wonder, which would suggest that the phrase had been well in vogue before Kemp used it.