When I was in high school there was a hallway that I would not walk into. It was where all the auto classes were held, and while it was really great that our school even offered classes like that soooo many of those students would use chewing tobacco and they didn't give a fuck. Spat their nasty gross black spit all over the walls and floor. I felt bad for the ceramics classes because they shared that hallway. Part of it was concrete and part was carpet, but they didn't discriminate.
Not good if you're wanting to walk in the area. Especially for me, because I was barefoot quite a bit at school. Ugh.
Stuff should be illegal just because it's gross. Makes me actually sick to my stomach to see someone spit up a gross glob of black/brown stuff.