frown, scowl
嚬 centers on a facial expression of displeasure: frowning or scowling, often with the mouth involved.
嚬 combines 口 (mouth) with 頻, which likely contributes the sound and may relate to repeated or drawn-together movement, suggesting a frowning mouth.
The mouth 口 beside 頻 (which can suggest repetition or frequency) gives the image of a mouth repeatedly tightening into a frown or scowl.
For ヒン, imagine a person frowning so hard their mouth makes a sharp 'hin' sound of displeasure: hin -> ヒン.