The same change can be made to each of the words below to create new ones. Can you determine what it is?

STY
STIR
STRING
STINTING

HINT:
Remove two letters from each word and replace them with two different letters.

Answers:

The ST in each word can be replace by PA:

PAY
PAIR
PARING
PAINTING

Credit: NY Times Crossword
Patrick Merrell
March 17, 2010 (St. Patrick's Day)


NOTE: This is called the ST/PA trick