What do the following words have in common?

BALL
LOCK
JACK
BUFF
PICK
MARK

HINT:
The same two letters will change each word into a new one.

Answer:

The letters ET can be added to each word to change it into a new one:

BALLET
LOCKET
JACKET
BUFFET
PICKET
MARKET

Credit: LA Times Crossword
July 26, 2015
Melanie Miller
CLOSE ENCOUNTERS