Basically it's a place where the line between dimensions is thin, and in this case there's a really really bad and evil place close to Earth. So the evil energy leaks out and makes things all wiggy and more likely to go wrong or strange.
[Look, he's guessing this...whoever this is is pretty innocent. He's not explaining Hell in detail to them.]
I did not know I needed these interactions!
[Look, he's guessing this...whoever this is is pretty innocent. He's not explaining Hell in detail to them.]