why does percy at the beggining of book 4 say when he sees rachel at the skool:my redhed nightmare?

Cause she recognizes him and can see through the mist

I'm pretty sure he says that cause she wouldn't stop asking questions about him at the dam

If you can recall in book 3 Percy meets Rachel Elizabeth Dare at the Hoover Dam. When Percy meets Rachel he is with riptide and Rachel could see through the mist, and so I guess he just remembers her and know she sees through the mist......? Dunno, I have to read the 3rd and 4th book again. Anyways I hope this helps!
~Diana