American English includes one of the rarest sounds on Earth, but we use it all the time
Er…this is odd.

Learning to make sounds we didn't grow up with can be tricky.
When (or if) kids learn phonics at school, they're taught the symbols that go with sounds of their country's native language or languages. People all around the world grow up learning to make specific sounds with their mouths by imitating the language(s) they are immersed in, which can leave us completely unaware of how many other sounds there are until we hear a language that's far different from our own.
Even the common foreign languages that American school kids learn have sounds that can be tricky to get down. The rolled "r" in Spanish. The nuances of French vowel pronunciations. The glottal stops in German. The sound that's a mix between "r" and "l" in Japanese. And for people learning English, one of the trickiest sounds to get down is "er," as in the American pronunciation of "bird," "world," "summer," or "percent."
Oddly enough, for as common as the "er" sound is in English, it's linguistically rare. According to the Linguistics Channel @human1011, the "er" sound is found in less than 1% of the world's languages, rarer than the click consonants found in some languages in East and Southern Africa.
- YouTubewww.youtube.com
As rare as the sound is, there are a lot of people in the world who use it, mainly because it's also used in Mandarin Chinese, or at least many variations of it. So, while there aren't many languages that use it, by sheer numbers of people, it's not that uncommon.
"So, a sound that's so rare that it's in less than 1% of the world's languages just happens to exist in the two most spoken languages on Earth? Can that really be a coincidence?" the @human1011 video asks. Well, yes. English and Chinese don't share a common linguistic root, so those sounds just happened to evolve in very different parts of the planet. According to some people in the comments of the video, there are regional dialects in Brazil where the "er" sound is used and in certain parts of the Netherlands as well.
Pronouncing the "er" sound is hard if you don't grow up with it, largely because it's all about the placement and shape of the tongue inside the mouth combined with the way the lips are positioned. That combination is physically tricky to show someone. This video, from a non-native-English-speaker does a good job of explaining the mouth movements that create the sound.
- YouTubewww.youtube.com
What's particularly interesting about the "er" sound in American English is that it functions as a vowel sound. Most of us learned that the vowels in English are a, e, i, o, u, and sometimes y, and that's true as far as written vowels go, but vowel sounds are different. In the word "bird," the letter "i" is a vowel, but doesn't make any of the "i" sounds that we learned in school. Instead, the "ir" combine to make the "er" vowel sound. It's called an r-controlled vowel, and we see it in tons of words like "work," "were," "burn," "skirt," etc.
Learn something new every day, right?
Here's another video that explains the physical aspects of articulating the r-controlled vowel sound.
- YouTubewww.youtube.com
Most of us don't think about the fact that sounds we pronounce without even thinking about it have to be specifically learned and practiced by people who didn't grow up with them. It's not until we start trying to learn a language that's different from our own that we see how many sounds we have to work hard to make, sometimes even having to train our mouth muscles in ways they've never been used before.
It's also a good reminder to be patient and kind with people who are learning a language. It's not easy, and anyone making an effort to communicate in someone else's language deserves our grace and kudos.
You can follow @human1011 on YouTube for more interesting linguistics trivia.