Present participle of crumple; the ongoing action of wrinkling, crushing, or folding something.
From the verb 'crumple' with the present participle suffix '-ing'; follows standard English patterns for marking continuous actions.
The sound and feel of 'crumpling' actually matches its pronunciation—the repeated 'm' and 'p' sounds make the word feel like the action it describes, which is called phonaesthesia.
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