1. What do the following words have in common?

ANGLE
KNEW
GRIST

2. What do the following words have in common?

STONE
SHIVER
SEATS
FLIES
THEIRS

HINTS:
1. Changing one letter is each word will create three new, related words.
2. It has to do with removing letters.

Answers:

Changing one letter in each word gives

ANKLE
KNEE
WRIST

2. Removing the first and  last letter of each word still leaves a valid word:

TON / HIVE / EAT / LIE / HEIR