Haha! Lucky me! I don't have to fill this!
When you drop an item on the ground, if it has pixels near the bottom, it will actually appear to go into the ground.
How to reproduce:
Drop an item with pixels near the bottom such as an apple onto a block.
Sorry if that was a little confusing, if you didn't understand that then you should be able to see what I'm talking about by looking at my pic.