- Tripwire (one of several)

I wanted Nanase to have to roll for something, but I didn’t want it to be for whether she springs the trap.

She’s solved the mini-puzzle Ellen gave her, and her reward is to spring the trap. That doesn’t require a roll.

Given that there’s about to be heavy things falling from ceiling, however, she needs to roll far enough to not get caught up in it herself. THAT she has to roll for.