For it is dark in the hole 

Erwin is an expert. Nobody knows holes like he does. He identifies them where others only see a stain, he detects life-threatening condition which an amateur overlooks in ignorance. At least in his reality. The reality of his girlfriend looks strikingly different. Especially when both of them are invited to a dinner. Here Erwin is treated unsympathetically when he tries to convince the hosts that a perceived stain on the wall is in fact a dangerous hole. Who is owning reality anyway? And how dangerous can such a hole actually be?