Some nice ideas. Did you mean "saw wood" or "wood saw" in the group with mirk, worm and dead? Normally you'd want the extra word to go always at the front or always at the end, but I don't think "saw wood" is really a thing. For that group and the silk group, you haven't actually given the answer.

Yes, agree with Dangermouse - explanations need a lot of work and what's a "burth"? Tough grid.

Saw wood means snore in USA. Sorry

Saw wood is fine, its how you make bigger wood into smaller wood, not a spelling contest either.