It was a bank. A piggy bank. Common in shape, usual in form, except with a catch: drop money in, it "disappears". The reason I type that in "quotation marks" is because the money got?wired somewhere else. For the little tot who owned this bank — let's call him Efflu ("Little Johnny" has been used too many times) — he was raised in an ultrawealthy family, and had no shortage of allowance. So, he'd take his Pop's vintage coin collections and drop them, piece by piece, into the slot, each landing with a satisfying ker-thunk! Of course, when Efflu went to open up the piggy bank at the bottom and unscrew the taut circle that prevented Mr. Piggie's guts from dropping out, the sound was that of a faintly stale, mellow air. And nothing was ever seen inside.
Efflu kept this to himself.?At his young age, he didn't know this was not how the world was supposed to work — at least, according to the grown-uppers around him. Ah, Efflu's Pop had so many coins, so he never noticed any of them missing. Not his rare China Blue?collection. Not the limited-edition, pseudo-commemorative set issued when Quebec became a floating island in '13. And so, the lad kept dropping coins in.
Eventually, dollar bills and that sort of thing began to be descended into the tight porcelain slit of the pig's back. They didn't land with such a noise — unless the bill was used as a snug cocoon for the nickels and dimes and much, much more — in that case, there might be a muffled thud not unlike a crisp heap of snow falling from the awnings of a remote cabin.
Ker-thunk! Ka-chunk! P-plunk!
And so it went.
Efflu never found out the money ended up feeding his parallel self in an alternative universe.