Funny that you mention that....
A little OT , but.... when my son was about 8 months old, I got out the cassette recorder and was taping him. Got all the babbling and crys.
I was playing the tape back while he was crying and it got to the part of the tape with the crys....AND wham !!! He stopped dead cold as soon as he heard himself cry. He stopped and looked around like "who is that ??"
I tried it again next time he had a tantrum , worked again.
He never cried again unless it really was warranted.