One of the characteristics of Japanese language is its abundant variety of onomatopoeia. It’s a group of adjectives and adverbs used to describe the state or sound of something, typically with the same syllable repeated (among other formations).
In many languages, words are created by imitating the sound of animals, but you can express more than just those sounds in Japanese.
For example, your heart goes ドキドキ doki-doki (pounding) right before an important interview, you feel ふわふわ fuwa-fuwa (soft) when you touch that fluffy white little dog, and the snow falls しんしん shin-shin (endlessly and quietly).
English, for example, has rich variety of verbs to describe the intensity of an action that would be expressed by onomatopoeia in Japanese. Take cry 泣く for instance to show how onomatopoeia works:
Cry (out loud): エンエン en-en / ワンワン wan-wan 泣く
Shed tears: ポロポロ poro-poro / ボロボロ boro-boro 泣く
Weep: シクシク shiku-shiku 泣く
Sob: メソメソ meso-meso 泣く
Whine: ピーピー pii-pii 泣く
Whereas English uses completely different words to express different types of crying, Japanese main verb 泣く remains the same, but it is combined with different adverbs.
The meaning of each onomatopoeia is practically universal among native Japanese speakers. Besides, even one can make up a new onomatopoeia for a specific situation, making others get the sense of how the crying is.
So, if he is crying intensely, you might want to say ダーダー daa-daa, or if she is sobbing with hiccups, you could say グスグス gusu-gusu and everyone can understand what you mean. I think this has something to do with the reason emojis developed in Japan. The onomatopoeia add vivid picture to a text, just as the emojis do.
There is a certain association between the sound and movement/state/feeling across the human languages. Generally speaking, the sound “k” gives hard and small connotation where “g” sound is related to somehow bigger and/or heavy, “m” brings up in your mind something round or slow in movement etc.
For Japanese people, this association is even tighter and is already a part of its culture. That is why, it is said that acquiring the actual sense/feeling of the onomatopoeia and utilize them freely and correctly takes time even for the advanced Japanese learners.
Can you tell the difference between しわしわ shiwa-shiwa and しゅわしゅわ shuwa-shuwa?
(Answer: wrinkly vs. bubbly like champagne)