I absolutely loved a friend’s response, “Maybe it’s not oil. Maybe it’s an evil stain.” Someone else mentioned maybe something smells wrong there or maybe there are open underground lines that we don’t notice, but she senses. I was going for the mundane explanations, rather than the less mundane paranormal explanations, like my friend’s “evil stain” theory. Haha!
I like the Evil Stain Theory! Obviously the fabric of space/time was punctured by some nefarious, trans-galactic stiletto allowing an inter-dimensional, oleaginous hippo to escape and become one with the sidewalk...