Smoke came from his mouth and blue flames from his eyes.

There was a sulphurous odor about him.

He was first seen rising out of the spring-hole, and there is a passage in the bottom of the spring-hole that leads straight down to hell.

Solomon is my authority.
"I asked him how he explained the apparition and he reckoned it was the ghost of the slave who was beaten to death, and that since his old master had come back to haunt the laurel walk, he had come back to haunt his old master.

That sounds to me like a plausible explanation.