Minecraft wiki entry for Hopper, associated text: A hopper with a storage container above it (such as a furnace, chest, dropper, composter, or another hopper) attempts to pull from the container instead of checking for floating items above it, and hence can not collect items. A hopper always tries to push or pull items using the leftmost available slot. When a hopper is removing items from a chest, the items disappear from left to right. Similarly, when filling up a chest, the chest fills up from left to right. Hoppers prioritize pulling from the first slot of a container over pulling into the first hopper slot. If a hopper has stone in its first slot and nothing in its second while the container it is pulling from has chicken in its first slot but stone in the second, the hopper pulls the chicken from the first slot of the container into its empty second slot. However, if the hopper is unable to pull the chicken, such as if all slots are filled with stone, the hopper pulls the stone from the second slot of the container instead. Similarly, hoppers prioritize pushing from their first slot over pushing into the first slot of a container. If a hopper has stone in its first slot and chicken in its second while the container it is pushing to has chicken it its first slot but stone in the second, the hopper pushes stone from its first slot into the second slot of the container.