On this show , we explore the origins and usage of common expressions in American English . Sometimes we tie the show to an event or special time of the year . This show could be tied to any time of the year that features a holiday . Holidays are a wonderful time of the year ! They are a time when people slow down and take a break from their daily lives . While holidays are celebrated in different ways , many have something in common -- gift-giving ! And who doesn't like to get a present . Covered in pretty paper , maybe tied with a bow or ribbon , a wrapped gift is a surprise . It could be anything ! "Oh , you really shouldn't have !" is a common response when someone hands you a gift . We say this even when we are thinking to ourselves , “Yay ! I got a present !” Sometimes the gift is perfect . "It's just what I have always wanted !" you might say . Sometimes it's not . We have all been there . You happily tear open a gift , wondering what is inside . But then you see it and you are ... disappointed . But you must not show it . And you absolutely must not criticize the gift and make comments about why you don't like it . In other words , don't look a gift horse in the mouth . This idiom is really old . However , some word experts say the idiom is much older than that . However old it is , people must have used it when gifting a horse was a common thing . To understand this idiom , we must understand a bit about horse's teeth . They grow over time . So , checking the length of the teeth is a way of knowing the horse's age . Although I have never given or received a horse , I'm guessing a young horse makes a better gift than an old one . However , checking the horse's mouth would be a sign of mistrust towards the gift giver . This would be bad manners . And it might make the giver feel embarrassed or even angry ! The polite thing to do is simply to say "thank you " and accept the gift horse graciously . These days , horses are not common gifts . But we commonly use this idiom . Don't be ungrateful when you receive a present , even if it's not exactly what you wanted . Besides gifts , you can use this idiom for other things , such as a favor . She comes to the dinner , smiling from ear to ear , and hands you the dish she has cooked . It is very burnt and it smells ... odd . But you don't want to look a gift horse in the mouth . You thank her for her dish and the time she took to make it . Then you put it on the table ... in the back ... where people hopefully won't see it . After all , it's the thought that counts . This means that it's the thought of gift-giving and not the gift itself that is important . And don't worry . Have you ever received a gift that you didn't like ?