Penny suddenly sat up very straight, listening intently.
From some distance away came a faint, metallic pounding sound.
“What’s that noise?” she asked, puzzled.
The old trapper also was listening alertly.
Again the strange noise was repeated. Bing-ping-ping! Ping-ping!
“It sounds like someone pounding on a sheet of metal!” exclaimed Penny. “I’d say it’s coming from the edge of the swamp—perhaps Lookout Island!”
The trapper nodded, still listening.
Again they heard the pounding which seemed in a queer pattern of dots and dashes.
“It’s a code!” Penny declared excitedly. “Perhaps a message is being sent to someone hiding here in the swamp!”
“In all the times I’ve been in these waters, I never before heard nothin’ like that,” the guide admitted. “I wonder—”