A new storage block: the slime casing

The slime casing is a special type of storage block crafted from 8 slime balls (or maybe it's dimensional versions). It is like a hopper, but no GUI. So, it impossible to put items it or out normally. To put things in, you must drop it on top of the slime casing. It has only 3 slots. To take things out, you have to break it. It will drop nothing when mined, unless you have silk touch then it will drop 8 slime balls. This block has 2 main uses: the fact that you don't know what's inside without breaking it and you can't get what's inside without breaking it. This mechanic can be used for puzzles, trap, shops etc. (Note: should whatever is inside a slime casing be extractable by hoppers. I'm not sure whether including this feature is good