Minecraft wiki entry for Honey_Block, associated text: A honey block adjacent to a block that cannot be moved by pistons ignores the immobile block. However, if an adjacent block could be moved but is prevented by the presence of an immobile block, the honey block is also prevented from moving. Liquids are an exception: they are not moved, but neither do they stop a piston from pushing or pulling blocks into their space (usually destroying the liquid, and in a rare case displacing it through the piston). Honey blocks, unlike slime blocks, cannot have a redstone signal sent through them via a repeater or an observer, etc.