I profiled this activity back in November 2009 for the CIF Newsletter after finding it on the internet. Since then I've found myself playing it more and more and teaching it to others.

1. Start with a 5-letter word.
2. Change one of the five letters to create a new word.
3. Continue changing one letter at a time to see how many new words you can create.

1. You may not change the same letter position twice in a row. (If you notice in the grid above, the boxes of the letter being changed are in bold. No two are in the same position consecutively.)
2. Starting in line 2, once you have substituted a particular letter it is no longer available. (The Used Letter column to the right of the grid keeps a running tally of each substituted letter. Notice how they do not repeat.)

You earn 1 point  for changing the first position (ex: Stone --> Atone)
You earn 2 points for changing the second position (ex: sPars --> sCars)
You earn 3 points for changing the third position (ex: stAre --> stOre)
You earn 4 points for changing the fourth position (ex: spaCe --> spaRe)
You earn 5 points for changing the fifth position (ex: scarS --> scarE)