In several levels in the game, there are Shy Guys which are flying in the air with a red sack beneath them. Normally, if you eat or kill the Shy Guy, it will drop the Red Coin. If it drops the Red Coin, but you don't pick it up and instead run off-screen, you can then return to where the Shy Guy appeared. The Red Coin will be there still, but that Shy Guy will come in holding yet another Red Coin.