Whenever you move something that’s been in situ on the ground for a a wee while, you need to be careful you’re not causing undue disturbance to creatures that have set up home underneath it.
Usually that’s limited to all manner of worms, beetles, centipedes and millipedes and the occasional amphibian, all of which are able to move home relatively easily. At the first hint of daylight striking their former home they scurry off into the nearest shadows and into safety, while the worms start burrowing down into the damp soil.
Occasionally though, you find something else. Something that can’t move home quite as easily.