Why Juice Boxes Make Lousy Blocks

So while I was trying to make dinner yesterday, Jacob emptied all the 1-ish litre apple juice boxes from the cupboard. We had just recently bought a new case so there was probably 11 or 12 in there. At first it didn't really bother me. He was stacking them around Daniel and they both seemed to be entertained, which was a good thing. Who knew you could make walls and towers out of juice boxes? I guess I wasn't paying close enough attention because next thing I know Jacob is standing on top of his stack of juice boxes and the bottom two have broken open. Now the mess could have been much worse, which I am thankful for, but now I have discovered one more thing that needs to be kept in a locked cupboard... juice.