Cut a large ring out of card stock. Tie threads onto two tree ornaments. Pull both threads through a small metal ring and knot the ends together inside the paper ring. And now try to free the ornaments without untying the threads.
Solution: fold the paper ring in half.
Slip the metal ring onto the folded paper ring, pass it along the whole length and remove it.
Unfold the paper ring.
Now the ornaments can be easily freed from the paper ring. Simple!