Over the years, I have found all kinds of interesting things inside
pianos. Mainly tools left by a prior tuner, pencils, paper clips,
pens and usual things.
One time I received a call to service a piano that sounded strange.
It seems someone in the household tipped the bottle a bit much, and
when I removed the bottom board, I discovered about 30 empty whiskey
bottles. Some were touching the bass strings.
In another I found several boxes of condoms! These apparently had been
stored by a teen-age boy, who entered the room just as I found what was
causing a problem within the piano. He was very embarrassed that I had
discovered them, but I reassured him I would not reveal his hiding
place to his parents. I suggested he place them where they would not
interfere with the piano action, and calmly went on about my work.
Probably the most frightening thing was a live rat which jumped right
out and landed on my shoulder!
Pianos in public places suffer the most. Ash trays emptied into them,
and one had it's hammers liberally sprinkled with Worcestershire sauce!
I have seen drinks deliberately poured into the inside of a piano.
"Yeah, the piano needs a drink -- Splash!"