In The Great Gatsby Why does Nick refer to his servant Finn as demoniac?

Oh honey, Nick calling his servant Finn "demoniac" in The Great Gatsby is just a fancy way of saying the guy is a bit wild and intense. It's like saying Finn has a devilish energy about him, not that he's actually possessed by a demon. Nick's just being dramatic, like we all are after a few too many cocktails at a Gatsby party.