Nagen Nagen

J knows quite a few words now, but there's one, usually repeated, that particularly puzzles us.

Me: He just did it again.
W: What?
Me: The whole 'nagen nagen' thing. I can't work it what it means.
W: He does it a lot.
Me: It sounds very Scandiwegian. I feel like there should be subtitles whenever he speaks. Maybe he's auditioning for a part in one of those bleak Danish TV series?
W: Heh. There's actually an Australian mythological creature called the Nargun.
Me: No?!
W: Yes, really.
Me: And he's half Australian... could he be channelling something?
W: I don't think so.
Me: Ah well, back to the subtitling thing then...
W: Eh?
Me: Could we get a baby translator? My Mum told me that she used to translate what I said as a baby for my grandparents. I guess only a parent really knows what their kid is saying.
W: Except in this case.
Me: Yes, we've drawn a blank on this one.