This thing all things devours,
Birds, beasts, trees, and flowers.
Gnaws iron bites steel,
Grinds hard stones to meal,
Slays king, ruins town,
And beats high mountain down.
Answer: Time.
This riddle appears in the following downloadable PDF files:
Can you solve one of the most famous logic puzzle ever?
Memory Matching game for kids, adults and seniors.
Connect the matching tiles and pop them all.