[ She could hear his HP drop? (No, Yosuke.) He's just assuming she's got some sort of special abilities, some "know how". Maybe she's like Rise? Who knows. Either way, he's learned that this place has people from all walks of life and even different planets, so it's best to expect the unexpected.

Should they have expected this?

When the hallway leads them to the central area, his flashlight first hits the building. Yosuke pauses, his eyes widening a bit after a few seconds. ]

Is it just me, or is it louder in here? [ He steps forward, scanning the area. The light ends at the entrances of each of the tunnels, the rest of their depth plunging into darkness. ] Looks like we've got more tunnels. [ He turns his attention back to the building. ] ...You think this is the base of sewer operations? Or just a way station?

[ Or the Ninja Turtles HQ? ]