With a shrill shriek the lad brought the stick down on the long-eared animal's rump with a whack that, while it could not have hurt, did all that he had hoped it might.
Both the mule's hind feet shot up into the air, while the beast with a short, sharp bray of fright lunged straight ahead.
The guide uttered a shrill exclamation of warning as he saw the mule tearing through the bushes to the left of the trail. Leaving his two pack animals, Eagle-eye leaped for the fleeing one.
But he was too late.
All at once the frightened beast appeared to stand on his head, his hind feet beating a tattoo in the air; then he disappeared altogether.
The Pony Rider Boys, hearing the disturbance, had hurried up, and just in time to see the final scene in the little tragedy that their companion had caused.
"What's this? What's this?" demanded the Professor. "What's the matter?"
"Pony fall down! Pony fall down!" exclaimed the Indian, with a trace of excitement in his tone.
"He means our long-eared friend has taken a header over that rock there," Ned Rector informed them.
"I am afraid it is more serious than that," added Tad. "It looked to me as if the pack mule went over a cliff."