Board Thread:General Discussion/@comment-26006155-20181229180615/@comment-26006155-20190127090310

Amassador, you do have a point in that while it started as human technology, the monsters are building their own phones now, and probably have their own call numbering system.

And the monster population is a managable size. The ending chart has Sans remember that after you kill 20 monsters, there's a lot more space. So it's large, but not huge.

The monster population does seem to be increasing over time. There are a few references to how the City of New Home is becoming crowed. Hip Jukebox Horse at Grillby's remarks that he's worred about the erosion of local culture as more people move in from the city.

It would be nice to know what the monster population was when the Waterfall Glyphs were made, stating that it would take almost all of the monster souls in the Underground to equal the power of a single human SOUL. If the population is a lot higher now, this would be more easily achievable.

Even if Sans is using Timey Wimey hijinks to give Frisk the key.. the key to his room (and by that access, the key to the Silver Key Machine out back) must be one of the most secret and precious things Sans owns. This isn't something he would give to any human... only to someone really special.