By this time the swimmers were nearly together and all three stared ahead with painful intentness.
"That dark thing?" inquired Greer in an undertone,
"Yes, we ought to have a knife apiece."
"I never saw a shark lying still," panted Caradoc straining his eyes.
"Say, that's a little streak of seaweed," decided Farnol, beginning to move toward it.
Then all three perceived it was merely seaweed. The shark-like illusion disappeared completely the moment someone doubted it.
"Who cried out sharks anyway?" demanded Smith of Madden.
"Greer there warned me—he yelled 'school of sharks.'"
"Where did you see them?" inquired Caradoc of Farnol.
"You shouted school of sharks to me yourself," defended Greer.