Ah - brings back memories of snake set at inhuman speed. Normal was almost inhuman (level nine was particularly frustrating on normal). I turned my keyboard upside down for level 8 - remapping the keys to make things "difficult" is just plain annoying (it use to be cute, and then computers got good - and it's now just lazy game design). Mirror levels are a great idea.
I get a feeling you may need instructions for those who have never played snake... and possibly more in-game motivation to play for these players too. (I thought Nokia was still putting it on their phones... oh wait - damn smartphones don't come with anything cool pre-installed.)
It's only nine levels! So don't give up at Level 7! You're almost there!!