The same two changes can be made to each of the four words below to produce eight new words. Can you determine what  the two changes are?

IN
IT
ILL
ITCH

Answers:

Each word can be preceded by W to make four new words, and those words can in turn be preceded by T to make four more new words:

IN - WIN - TWIN
IT - WIT - TWIT
ILL - WILL - TWILL
ITCH - WITCH - TWITCH