It holds most knowledge that has ever been said.
But is not the brain, is not the head.
To feathers and their masters, it's both bane and boon.
One empty, and one full.
Answer: Paper.
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.