The public at Liverpool Street train station in London had a spontaneous reaction when the Olympic opening ceremonies at the TV screens reached "Hey Jude".
Similarly to the failing microphone on "Let It Be" during Live Aid back in 1985, McCartney's appearance on the opening of the olympics had issues. McCartney was supposed to partially mime his performance. His live vocals were the ones that would be heard in the stadium, while his pre-recorded studio-perfect vocals were to accompany the television broadcast. 'The End' went great: the 3 lines were lipsynched perfectly. The live vocals could be heard in the stadium, and his pre-recorded vocals was on TV. Then drummer Abe Jr. started counting off with his hi-hat, very likely hearing the click-track provided by musical director of the band and keyboard player Paul "Wix" Wickens in his ears. McCartney may also had in-ear monitors with the click-track for this occasion, it would make sense since he had to start the song, and he immediately realized what was going on. Then trouble began: McCartney started one bar and a half too soon with playing, resulting in hearing the audio on television as planned: just like on 'The End' no 'live' direct feed from the stage with only the stadium atmosphere microphones on, pre-recorded audio on full. But since those were out-of-sync because of McCartney missing the cue, you could hear a disastrous mix of them playing 'Hey Jude' in the stadium, with a bit later the pre-recorded version. Quickly the television audio crew turned off the backing track, and turned on the live band and vocals. If you look at the band members during the very first seconds of the song, notice Wix possibly trying to save something by skipping the backing track a bar and a half, which is technically possible. So that's what we heard at the live worldwide broadcast. Of course, for the tape-delayed butchered NBC version on the American television, this was 'fixed' by muting the pre-recorded 'backing track' from the very start. This resulted in hearing McCartney noticeable laughing about the huge mess-up, because he undoubtedly knew what happened.
Thanks to "nobodytoldme" for explaning what happened. And clearly, the mix-up didn't matter to the audience over on Liverpool Street Station.