Holloway picked up the crystal cube. "Did you question the children much?"
Paradine said, "Yeah. Scott said there were people in that cube when he first looked. I asked him what was in it now."
"What did he say?" The psychologist's eyes widened.
"He said they were building a place. His exact words. I asked him who — people? But he couldn't explain."

Mimsy Were The Borogoves (1943)