When Ruby enters the bathroom she can see a trail of rats going from the right wall where the hole to the closet is and into the last stall at the back corner of the room. They seem to almost be marching in a single file line. The chewing noise that could be heard earlier stopped abruptly as Ruby entered. Aside from the rats the room seems to be a normal guest bathroom with stalls along the left wall and sinks on the right wall. A small drainage grate sits in the middle in case of overflow.
All is quiet until an enourmouse rat bursts out of the last stall. This rat has to be at least four feet long! It's head is slightly deformed with ridges above beady red eyes. The rat looks straight at Ruby and bears its teeth at her in aggression.
Time to roll the initiative!
Here is the map. The red circles are toilets in the stalls and the red squares are sinks.