system
Given the following post, respond as if you're commenting on Reddit:
human
[The Cabin in the Woods] What is the use of the gory painting and the two-way mirror hidden beneath?

It seems obvious that someone would want to remove the hiddeous painting in the bedroom that Holden initially occupies. Therefore, it can be assumed that the technicians want the occupant to reveal the two-way mirror beneath. What advantage does this give the technicians and how does it help the ritual?
gpt
Remember the Harbinger?  The creepy dude at the gas station?  The ritual doesn't just require killing the people.  It requires them to transgress and be punished, and the transgression requires them to be warned.

Lots of the 'furniture', for lack of a better word, is not functional in the sense that it helps the technicians, but important for giving the five warnings that they ignore.  The dude at the gas station is one, the creepy furnishings are another.  It's all meant to add up to a scenario in which they *should* leave, but don't.  Therefore, transgression and punishment.