I think I would also take the case off the radio to ensure it also has not been used as a piggy bank. To be fair the cd versions tend to be more of a kid magnet and have found biscuits, bank cards, kids plastic cd's and coins in the past.
I wonder if there was ever a thread about the weirdest thing you found in the car? I'm trying to recall what it was for me, but two fully operational wasp nests under the bonnet of my Audi GT Coupe after I left it neglected for a year is close to the top.
Oh no, I think I got a winner.... I bought a beater to go around when I moved to Kuwait and found dozens of artificial nails and eyelashes of various colours all over the cabin area and various compartments.