Minecraft wiki entry for Unused_textures, associated text: debug.png could be made to appear in-game in certain Java Edition 1.13 snapshots due to being defined as the particle texture for bubble columns, meaning actions that would result in the creation of particles (such as falling from a height onto the edge of a block next to a bubble column) would show particles with this texture. They could also be seen when the bubble column was pushed by a piston.[14]