Not only was "I'm Not in Love", a classic pop record, but 10cc did something unique:
There's a section where a woman says "be quiet, big boys don't cry, big boys don't cry, big boys don't cry..." She was not a member of the band! She was a secretary in the music studio and 10cc needed someone to do a short female voice part. They couldn't find anyone. So they saw her and asked her; she said are you serious, I can't sing! The guys said that doesn't matter and she said OK.
That is amazing! She was interviewed about 2 years ago about it. Props for the guys for doing that! That was some serious guts. They could have taken the easy way out and got a sample from their label. But they just grabbed her and said you can do it!! Oh man that is cool.
So my question is was this unique? Has any other band [not just pop] ever grabbed someone who was there who was not musical and said "we need you to do a few lyrics!" I can't think of another example offhand.