The same two letters, in the same, consecutive order, will change each of the words below into new ones. What are the two letters and what are the new words?

REST
SING
CLING
BLING

Answer:

The letters AW, when inserted in the appropriate place, will change each word into a new one:

RAWEST
SAWING
CLAWING
BAWLING

Credit:
Jay Hackney
"HOW CUTE!"