^Comes from the days when horses were the basic piece of farm equipement and transportation and duly routinely traded on marketplaces; checking the degree of wear on the animal's teeth is a good way to ballpark its actual age ergo overall condition and likely remaining useful lifespan, which might not always be what the seller claimed...
Goes without saying that doing that with a gift was more than a little rude given what it implied of your opinion on the giver, whence the figure of speech.
last edited at Apr 4, 2020 4:13PM
