The answers to the following clues will have something in common.

1. Blood-sucking fish
2. "While you were out" information
3. Frown
4. Friendly and polite
5. A thousand millions
6. Little by little

Answers to clues:

1. LAMPREY
2. MESSAGE
3. GRIMACE
4. CORDIAL
5. BILLION
6. GRADUAL

What they have in common:

Each word can be split into two words with an over-lapping letter between them:

1. LAM(P)REY
2. MES(S)AGE
3. GRI(M)ACE
4. COR(D)IAL
5. BIL(L)ION
6. GRA(D)UAL

Credit: Will Shortz
NPR Weekend Edition Sunday Puzzle
February 8, 2009 - LINKING LETTERS