Walk on the living, they don't even mumble. Walk on the dead, they mutter and grumble. What are they?

This clever riddle plays on our everyday experiences with nature. When you walk across a lawn of lush, green grass or step lightly on the fresh leaves of a plant, you'll notice a distinct lack of sound. These living parts of plants are full of water, making them soft, flexible, and quiet underfoot. Their resilience allows them to bend and spring back without making much noise, even when trodden upon.

The second part of the riddle, however, refers to what happens when these same plant elements complete their life cycle. As leaves die and fall from trees, or as grass withers and dries out, they lose their water content. This change in cellular structure makes them brittle and stiff. When you walk on a carpet of dry, fallen leaves in autumn or a patch of parched grass, the pressure causes them to crackle, crunch, and rustle. These distinct sounds are the "muttering and grumbling" the riddle describes, a natural symphony of decomposition.

This delightful contrast highlights the continuous cycle of life and death in the natural world. From the silent vitality of living foliage to the audible transformation of decaying matter, the simple act of walking can reveal the subtle yet profound changes occurring all around us. It’s a reminder that even the quietest parts of our environment have stories to tell, often through the sounds they make.