There's a cool sound in language called a voiceless velar fricative, which is a special type of consonant. This sound was once common in Old English. You can still hear it today in some English dialects, especially in Scotland, like in the word "loch." When linguists write this sound down, they use the letter ⟨x⟩ from the International Phonetic Alphabet.
Making this sound involves a few interesting things. It's a fricative, meaning you make it by squeezing air through a narrow gap in your mouth, which creates a whooshing sound. It's "velar" because you use the back of your tongue against the soft part at the back of the roof of your mouth. And it's "voiceless" because your vocal cords don't vibrate at all when you say it. The air only comes out of your mouth, not your nose, and it flows down the middle of your tongue.
This sound probably existed in Proto-Germanic, the really old language that all Germanic languages like English and German came from. Its presence there is part of something called Grimm's law, a famous set of sound changes in language history. Interestingly, in Modern Greek, this sound developed from an older sound that was present in Ancient Greek.
