The string arrangement reinforces the music's air of sadness within the groaning cello line that connects the two halves from the bridge, notably the "blue" seventh in the second bridge go (the Eperformed following the vocal line "I don't know / she would not say") and during the descending operate through the viola that segues the bridge back into the verses, mimicked by McCartney's vocal on the 2nd move in the bridge.
So there is certainly leakage there. Then I mentioned I'd do this site a string quartet. The musicians objected to twiddling with headphones, so I gave them Paul's voice and guitar on two speakers possibly aspect of their microphones. So you can find leakage of Paul's guitar and voice to the string tracks.
Immediately after recovering, he sings the Beatles tune "Yesterday" for his friends and discovers they have never heard about the Beatles.