[Of course she has a good idea about it, but since she does know, she's not about to bring it up either. Not that the miko would've asked why Marisa had decided not to go even if she hadn't known the answer.

She nods in agreement about there being fewer people in the way if another incident happened while this was going on.]

Yeah, that's one good thing about all this iron mine business.

[And Reimu has known Marisa way too long not to become suspicious when she notices her friend has stopped shoveling. So she turns around to look.]

Marisa, what are you doing?