 Why does the party run into duplicates of themselves?
DOUBLE TROUBLE by CARL JACOBI Grannie Annie, that waspish science-fiction writer, was in a jam again. What with red-spot fever, talking cockatoos and flagpole trees, I was running in circles—especially since Grannie became twins every now and then. [Transcriber's Note: This etext was produced from Planet Stories Spring 1945. They rose straight up like enormous cat-tails, with only a melon-shaped protuberance at the top to show they were a form of vegetation. He could be excused this time, however, for this was only our third day on Jupiter's Eighth Moon, and the country was still strange to us. If you haven't read her books, you've missed something. Blood-and-thunder as these books are, however, they have one redeeming feature—authenticity of background. Grannie Annie was the original research digger-upper, and when she laid the setting of a yarn on a star of the sixth magnitude, only a transportation-velocity of less than light could prevent her from visiting her "stage" in person. He was an old prospector Grannie had met, and he had become so attached to the authoress he now followed her wherever she went. As for Xartal, he was a Martian and was slated to do the illustrations for Grannie's new book. Five minutes after my ship had blasted down, the four of us met in the offices of Interstellar Voice . It's no use to the people of Earth but of untold value on Mars. I'm not up on the scientific reasons, but it seems that life on the red planet has developed with a supersonic method of vocal communication. The Martian speaks as the Earthman does, but he amplifies his thoughts' transmission by way of wave lengths as high as three million vibrations per second. "But up until now this moon is the only place where it can be found. So now here we were at the outer reaches of the Baldric, four travelers on foot with only the barest necessities in the way of equipment and supplies. Xartal, the Martian illustrator, already had a notebook in his hands and was sketching a likeness of the creature. Above us, the great disc of Jupiter began to descend toward the horizon. Down there, slowly toiling across the sand, advanced a party of four persons. Behind her strode a grizzled Earth man in a flop-brimmed hat, another Earth man, and a Martian.
 They're the cockatoos, copying their appearance.
 It's the Red Fever influencing their perception.  As Grannie Annie says, it's a form of mass hypnosis.  They're a mirage, a result of the Baldric.  They're the cockatoos, copying their appearance.