The backing track. They used take 20 for the bulk of the backing track, but the tag of that take was deemed subpar, Brian then had the band do a pickup starting at the tag (he might have rejiggered some instrumentation for it) which I think was two takes. Then he edited the body of take 20 with the tag pickup piece to create the full backing track, and then all that was mixed to mono in preparation for the vocal sessions.
Wow, thanks. It appeared that Brian used the splicing technique quite a lot even before the recording of “Good Vibrations”~
Certainly -- as did everyone else. It's a nice easy way to combine the best parts of different takes, very common from the very birth of magnetic tape recordings.
Case in point: I SAW HER STANDING THERE. The Fabs kill it on that one, but from the guitar solo out, it's a different take edited on (or maybe from after the solo - I forget which).