The one to arrive first would call the other by a loud whistle in close imitation of a quail.

The other would answer by a similar whistle.

One day when about to mount the tree and give his usual signal of recall, Paul discovered the professor, who had been sent after them, approaching.

Quickly he climbed into the tree and concealed himself in the dense foliage.

At this moment he heard Stockie's familiar signal quite near the rendezvous, and to his dismay, the professor, hidden behind a tree close by, repeated the quail call, thus leading the unsuspecting Stockie to his doom.