After the party scene, the children are singing "So long, Farewell" and each child comes up to sing a line as a solo. When the line comes up when the boy (I think it's Friedrich) sings "I leave and heave a sigh and say goodbye, GoodBYE" At the "BYE" part, he goes up to an octave, with a vibrato and it sounds too good. So, I listened carefully, and sure enough, there is a quick break in his voice before he hits that note, alluding to the fact that someone else hit that note for him and they edited it in. I don't know if anyone else heard that, but listen anyway. It's there.