To determine the part of speech, we'd need more context.
Possible interpretations:
* Verb: If used as an action, like "He was whiffling the ball," it would be a verb.
* Noun: If used as a thing, like "The whiffling was loud," it would be a noun.
* Adjective: If used to describe something, like "She had a whiffling smile," it would be an adjective.
* Adverb: If used to modify a verb, adjective, or other adverb, like "He walked whiffling down the street," it would be an adverb.
Please provide the sentence or context in which "whiffling" is used so we can accurately determine the part of speech.