At this point, fear is pretty much a Pavlovian Response for Mark. The guy has experienced so much crazy stuff since getting stuck on Mars that even the smallest thing gets transformed into a crazy disaster in his mind. He can't let his fear trip him up, however—he needs to keep his eyes on the prize.

The Hab's been through a lot. It's been blown up. It's been deflated. It's been covered—literally—with Mark's poop. It must stink. Despite all of this, Mark still feels an immense amount of comfort when he's there. It might be nasty, but it's a familiar kind of nasty.