This may or may not be intended game behavior, but let’s say you place down a block of wool on a block of wool. It, obviously, makes a “wool” sound. A block of iron would make a “metal” sound. But, if you place a block of wool on a block of iron, it makes a “wool” sound, and if you place a block of iron on a block of wool, it makes a “metal” sound, despite the fact that it’s the same collision.