Interstellar : It's not a ghost, It's gravity

Cooper found the secret about Murph's ghost. He came to a conclusion that its gravity and he is demonstrating it to Murph by tossing a coin in to the straight line formed by the dust and the coin falls only in the line.

Cooper : It's not a ghost.

              It's gravity.

Donald : You want to clean that up

              when you've finished praying to it?

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