Green’s Dictionary of Slang

listening flap n.

(Aus.) the ear.

1908

Bulletin (Sydney) 1 Oct. 14/3: ‘Ain’t cher goin’ t’ rustle up th’ rent, y’r curry-spotted Guy Fawkes?’ snarled the sport. ‘There’ll be a rent in y’r listenin’ flap if y’d don’t stifle y’r sob,’ growled th’ game-gatherer ominously.