The man suddenly shot up like a fountain, growing huge; he towered over them, until he seemed miles high and the giant structures Dave could see were only the turned-up toes of the man's shoes.
He shrunk and became tiny. 
mnli hypothesis: He shrunk and became tiny.  premise: The man suddenly shot up like a fountain, growing huge; he towered over them, until he seemed miles high and the giant structures Dave could see were only the turned-up toes of the man's shoes.