Just Traditional Japanese cooking. So, naturally, Reimu's never seen it before.

There's a Censor Circle in one of the words Reimu says (床〇ナ), so I had to guess. My initial impression is that Reimu thinks this has something to do with 床オナ (yuka-ona), which is, essentially, grinding one's junk on the floor. Marisa's dialog is literally "difficulty level high," so I made an approximation. There might be an alternate meaning I'm missing. Maybe something to do with too many degrees of separation?

What I've deduced Reimu's conclusion to be sounds completely ridiculous, since there's seemingly nothing connecting that thought to anything, so I'm hesitant to make that the final translation... buuut she's said stupider things when Dairi's involved. Actually, no, if that's correct, this might be the dumbest thing she's ever said. I need someone with more experience to confirm.