Finnish often uses variation in vowels to express versions and nuances of descriptive words. For example, both the Finnish verb purskahtaa and the corresponding English words “spurt” and “squirt” can be heard as imitating spurting or squirting sounds. Finnish also uses pärskähtää, pirskahtaa, and porskahtaa in similar meanings, with e.g. so that pirskahtaa refers to smaller effects—generally, the sound i tends to refer to small things in descriptive words. Especially in spoken language, you may encounter more variants, many of which are not in any dictionary but can still be intuitively understood, partly from their “sound”, partly from their being similar to some more common descriptive words.
Some descriptive words are clearly onomatopoetic, i.e. they sound like the thing they stand for, but more often, it is a matter of associations. It requires some interpretation to hear pärskähtää as sounding like spurting. As the examples show, different languages have different style for descriptive words. The English verbs “whizz” and “zip” are descriptive, and so is the Finnish verb suhahtaa, which means roughly the same, but plays with sounds differently, so to say.
Due to word inflection, descriptive words in Finnish have parts that are not descriptive but belong to the grammar, e.g. the personal suffix in the verb form suhahta|vat.
Descriptive verbs are often used in colorative constructs: combinations of a common verb in the I infinitive and a descriptive verb in a normally inflected form. For example, we can say hän käveli kotiin (he walked home), using just the common verb kävellä, but we can also use the more descriptive expression hän kävellä löntysti kotiin (he lumbered home). The descriptive verb löntystää means clumsy, slow walking; there are many other verbs that mean much the same, like laahustaa, lampsia, köntystää, tallustaa. The descriptive verb could be used alone, too: hän löntysti kotiin. A colorative construct paints the picture in steps: it first uses a common, simple, rather colorless word like kävellä, then adds color to it using a verb that can be intuitively understood by its phonetic shape, after you get used to the idea.