サッと: Mix of ひらがな and カタカナ in the same word?

Question

So, I've come across this sentence

そのとき、陽が当たった石版に何かの影がサッと横切った。

which I'm fairly sure it means something like

At that time, something's shadow quickly crossed the sunlit lithograph.

Now, what surprised me was the word サッと. I know that カタカナ is sometimes used to emphasise the word (much like an italic or bold font). What I didn't know is that there are words written in a mix of ひらがな and カタカナ.

A quick search revealed this answer. From what I could surmise, three groups of words were mentioned:

1. When the final word is made of two other words (e.g. あんパン is made from joining あん and パン)

2. Foreign words made into verbs (e.g. ググる from ググル, ダブる from ダブル), in which a final る is written in ひらがな

3. The same concept as 2. but for adjectives (e.g. セクしい from セクシー)

Now, サッと doesn't match neither group. From the context of the sentence, I've connected it with 颯っと which is usually written in kana alone, according to Jisho.

In summary, why the mix of ひらがな and カタカナ in this case?

Answer 1

Onomatopoeic words can generally function adverbially with or without と. However, for onomatopoeias ending in 〜っ, と is usually added.

Onomatopoeias can be written either in hiragana or in katakana, but as is common for grammatical particles the と will usually be written in hiragana.

See also

• What is the purpose of adding と?
• What does "fūtsu" mean?
• Does anyone knows the meaning of "モゾリと"?
• What does どぼり mean?