For those having trouble on level 17, because of holes with blue glue at the bottom, the word GARDEN is impossible. The word is the opposite of "safety".
I can tell that level 12 references the number 12 with white squares (not including some of the blocks) forming the number 12, the number blocks forming the number twelve, a word spelled "twelve," the level number, which is 12, and an animation for the number 12.
For those having trouble on level 2, because of a hole underneath the spot for the third letter of that word, the word BEDROOM is impossible, though you DO have to have a B at the beginning. The word you have to make is a kind of feeling from when there's no entertainment for you (you don't experience any fun at that time).