Hooking up Hoppers in such a way that an infinite loop is created, meaning two Hoppers pointing at eachother, constantly exchanging items (See picture) , will sometimes result in the itemcount of the item thrown (note: so far it only happened when the item was thrown into the Hopper, not put in from the players inventory) into the Hopper being increased by 1. So far, I have only tested this on singleplayer. However, if this works on multiplayer, this could be an unfair exploit.