It came through the heavy door and passed into the room before his eyes. The dying flame leapt up in the fireplace. It was the same face, the very same – Marley dressed as he had always dressed in his lifetime. The chain was wound around him and lay behind him like a tail. It was made of money-boxes, keys, locks, account books, business papers and money bags. Scrooge, as he looked at him, could see through his body. He could see the two buttons on Marley’s coat behind.
“Well?” said Scrooge as his cold voice, “What do you want with me?”
“Much!”
Yes , it was Marley’s voice.
“Who are you?”
“Ask me who I was!”
“Who were you then?” said Scrooge.
:“In life I was Jacob Marley. You do not believe in me,” said the Ghost.
No,” said Scrooge, “I do not.”
“You do not believe your eyes,”
“No,” said Scrooge. “I do not. I do not always trust my eyes: a little thing can affect one’s eyes. If I eat a bit of cheese or some meat which is not well cooked, it may make my eyes see things wrongly. Humbug, I tell you, humbug!”

At this, the Ghost gave a fearful cry and shook its chain with such a terrible noise that Scrooge held on to his chair to save himself from falling senseless. Then the Ghost took off the cloth which was tied round its head, and its mouth fell open like the mouth of a dead man.

Scrooge fell upon his knees and held his hands in front of his face. “Mercy!” he cried. “Why have you come to trouble me?”
“Now,” said the Ghost, “do you believe in me or not?”
“I do,” said Scrooge. “I do! But why must the spirits of the dead walk the earth, and why do they come to me?”
“Every man “answered the Ghost, “should in his lifetime walk among his fellow men and travel far. He should share their sorrows and their joys. But if a man’s spirit does not do this in life, then it must wander through the world after death and see what it can no longer share but might have shared on earth and turned to happiness,”

Again the Ghost gave a cry and shook its chain.
“You are chained!” said Scrooge, shaking with fear. “Tell me why?”
“I am wearing the chain which I made during my life,” replied the Ghost. “I made it, foot by foot, and bound it on myself of my own free will. Do you wish to know the weight and length of the chain which you yourself bear? It was as heavy and as long as this one seven Christmas Eves ago, and you have laboured on it since.”

“Tell me no more. Say something to comfort me, Jacob.”
“I have no comfort to give, the Ghost replied. “I cannot rest. I cannot stay here. I must go. In life, my spirit cannot walked outside the office, but now many weary journeys lie before me.”

“Seven years dead!” thought Scrooge, “and travelling all the time!”
“The whole time,” said the Ghost. “No rest. No peace. Do you not know that any Christian spirit finds its life on earth too short for the measureless chances of usefulness and no sorrow afterwards can pay for those chances which have been missed? But I, I missed them all.”

It took up the chain in its arms as if that was the cause of its grief and threw it heavily upon the floor.
Question
How could Scrooge tell immediately that this was not a real person?