I haven't worked inside accordions much but Inside computers, I have found dead mice, a well sizzled snake of about 15 inches and one even with 20 or so cockroaches. Does that count?
Wow, I have worked inside computers too and never found dead mice or snakes or even cockroaches. The worst I ever had to deal with was a large exploded capacitor (after someone plugged a 120V machine in a 220V outlet. Happened twice actually. With these large electrolytic capacitors that is a terrible mess to clean up.
Inside an accordion mold and rust (or other forms of corrosion) are the worst things I have seen. The Scotch tape was just the weirdest thing I saw, but did no harm.