I was just listening to a piece recorded some years ago, it's 5 songs but pretty much recorded as a single piece, certainly the last three songs. It was quite hard to mix, having to be done in one go and 21 minutes long but the last piece had two acoustics, an overdriven acoustic that sounded growly, a double bass, flute and two tracks of percussion.
I remember doing the percussion like it was yesterday, even though it was last century. My mate and I used various household objects like keys and the sound of scissors snipping. Listening back to the original tracks on headphones the other day, I noticed something I'd been completely unaware of for years, some congas. I must've totally forgotten about them because for the last goodness knows how many years, they've not formed any part of my memory of this piece.
They were buried in the mix.
I think the reason for that was twofold. Partly because, in order to get as much percussion on as possible, I put two separate mics on, one on me, one on my mate. We were down to our last two tracks of an 8 track portastudio so I put the mics through a mic mixer that split the signals {we were on opposite sides of the small room we recorded in in my then flat}. We tracked twice.
The other reason was that my miking was pretty shit in those days so the congas barely came out. So much so that I'd forgotten for a good 13 years that there were even congas on the piece until two days ago.
Sometimes for a joke, engineers would bury something deep in the mix so you wouldn't really notice it but the band would have a laugh knowing that some taboo word or a fart or whatever would play every time the song would play. For example, buried in the mix of the song "Hey Jude", you can hear Paul McCartney saying something like "fookin' 'ell" when he comes in a bit early.