I have been listening to the Beatle's "Lucy in the Sky with Diamonds"
over and over recently (per it's my daughter's favorite song).  Anyway, I
listened more closely then I had in a long time and I was struck by how cool
the backup vocals are during the chorus.  I assume this must be Paul but it
doesn't really sound like him to me. Thus, my little question. Is that Paul
singing back up and if not, who is it?  
Secondly, this got me wondering if as a band they used backup singers that
were "non Beatles".  I'm sure they must have but I can't think of any
songs...anyone?

Best, Steve