If a falling block entity falls onto a slime block attached to a piston, and the piston extends to launch the entity into the air, occasionally the entity will break and turn into an item of whatever block is was. This can be most easily replicated by building a piston on a 22 redstone-tick clock as shown below, placing two sand blocks on the slime block, and breaking the lower sand block just before the piston extends. The timing is a bit difficult to get right, but if the block is broken with the correct timing it will get launched in the air repeatedly before eventually breaking.