1. What do the following words have in common?

ADMIRER

CAFE NOIR

TOBOGGAN

MARSHMALLOW

2. What do the following words have in common?

TRACE

RATS

BLITZ

RISE

PRICE

CATER

HINTS:

1. Four related words are hidden in the clue words.

2. The same single letter will change each word to a new one.

Answers:

1. Hidden in each word is a swamp:

MIRE / FEN / BOG / MARSH 

2. Inserting an "N" in each word gives a new word:

TRANCE
RANTS
BLINTZ
RINSE
PRINCE
CANTER