Re-read the excerpt below. What inference is MOST likely?
On the fortieth day, Louie was lying beside Phil under the canopy when he abruptly sat up. He could hear singing. He kept listening; it sounded like a choir. He nudged Phil and asked him if he heard anything. Phil said no. Louie slid the canopy off and squinted into the daylight. The ocean was a featureless flatness. He looked up.
Above him, floating in a bright cloud, he saw human figures, silhouetted against the sky. He counted twenty-one of them. They were singing the sweetest song he had ever heard.
Louie stared up, astonished, listening to the singing. What he was seeing and hearing was impossible, and yet he felt absolutely lucid. This was, he felt certain, no hallucination, no vision. He sat under the singers, listening to their voices, memorizing the melody, until they faded away.
Phil had heard and seen nothing. Whatever this had been, Louie concluded, it belonged to him alone.