Someone is definitely going to shadow him all day just to be a pain in the ass. Maybe he considers it progress that Reaper isn't trying to murder him yet--or maybe he's just more concerned with the current situation. He'll take either.

So he's not comfortable, no, but he follows along anyway, still half-considering opening fire and seeing how quickly Reaper can regenerate when he's being pumped full of pulse munitions. And he's not stupid, either. Following Reaper into an enclosed space like this is most certainly a death sentence. He takes point outside the door as Reaper forces it open.

"Something in there?"

A death trap for him, perhaps?