1. What do the following words have in common?

CAPPED
LOSSES
MATTING
TAPPED
DOOMED

2. What do the following words have in common?

TRIPLE
THOUGH
DYE
HEART

Answers:

1. Dropping one of the double letters results in a new word:

CAPED / LOSES / MATING / TAPED / DOMED

2. Without dropping it, use the first letter of each word as the last letter, to get a new word:

TRIPLET / THOUGHT / DYED / HEARTH