So when I was ten years old my family had just moved into a new house, brand new just built and everything. A friend and I were in a small room, maybe 10 feet by 10 feet, playing a game of Magic The Gathering, he tossed a card at me, I missed my catch and it went behind me. I never could find it, ever. The room was completely empty, no furniture, nothing but carpet. I still have no idea where it went.
I have also lost many game CDs, or cartridges, no idea where they are, but it seems more plausible to lose them amongst my rooms, rather than losing a card in a completely empty, clean room.
Oh yeah, also when I had a pet ferret my shoes would dissapear, it took me a week or two to realize my ferret would actually take my shoes, and hide them under the couch. Sneaky bastard.