system
Given the following post, respond as if you're commenting on Reddit:
human
[Monsters Inc] How did they power the first ever door?

For anyone who is unfamiliar with the film Monsters Inc, It's based in some dimension where monsters are as technically advanced as human's although their electrical system is powered by childrens screams.

To obtain children's screams monsters go through doors into the human world to scare children.

These doors must be powered to work though... 

So my question, how did they power the first ever door to obtain screams?....
gpt
It could be that they had other sources of power but because children's screams are a clean, efficient and potentially limitless source of energy they moved to adopt it across their entire society. After all, there is no reason to pollute if renewable energy is easily available.