What do the following four-letter words have in common?

CAME
PEAR
EASE
PROW
HAZE
NAVE

Answers:

Adding an L at the end of each word changes it into a new one:

CAMEL
PEARL
EASEL
PROWL
HAZEL 
NAVEL 

Credit: 
NPR Weekend Edition Sunday Puzzle
June 5, 2010
Will Shortz