Each set of words below shares an interesting property. Can you determine what it is?

1. MANIC - PANIC

2. MANIA - MANOR

3. MINX - MANX

4. GLAD - GRID

5. DEAN - MEAN

6. BOOK - BONE

7. COLD - MOLD

8. WISH - CASH 

9. RAGA - RAIL

10. BARK - BALK

Answers:

Two letters of the first word in each set are a state postal abbreviation - replaced by the abbreviation of another state in the corresponding letters of the second word:

1. MAnic - PAnic

2. manIA - manOR

3. MInx - MAnx

4. gLAd - gRId

5. DEan - MEan

6. boOK - boNE

7. COld - MOld

8. WIsh - CAsh

9. raGA - raIL

10. bARk - bALk