godan verb (-ru), intransitive verb
hesitate to speak; mumble; hem and haw
Internet slang derived from the mimetic word もにょもにょ. Describes the state of being unable to speak clearly due to hesitation, embarrassment, or irritation, often with a sense of fidgeting or unease.
See also: もにょもにょ
I got nervous during the interview and ended up mumbling.
彼は何か言いたそうにもにょっていた。
He was hemming and hawing as if he wanted to say something.