Doublets

This is a word game. You take one word and transform it into another word of equal many letters. You replace one letter at a time, but make sure that you're always creating other actual words until you arrive at the desired end word.

It was invented by Lewis Carroll.

An example: Cat into Dog

CAT
COT
COG
DOG

When you're bored, try thinking of some yourself. It can be fun and mentally challenging and doesn't require even a pen and paper.