“The idea that anything that can be duplicated can be canceled,” he announced gloomily, “is unfortunately rot.  We can duplicate sounds, but there’s no way to make them cancel out!  Not accurately!”

Jill had eaten a substantial part of the porcupine while the newscast was on.  It was not a satisfying breakfast, but it cheered her immensely after two days of near-starvation.

“But,” she observed, “maybe that won’t apply to this business when you report what you know.  It’s not likely that anybody else has stood just outside a beam and made tests of what it’s like and how it’s aimed and so on.”

They started off.  For journeying in the Park, Lockley had the advantage that as part of the preparation for making a new map, he’d familiarized himself with all mapping done to date.  He knew very nearly where he was.  He knew within a close margin just where the terror beam stretched.  He’d smashed his watch, which during sunshine substituted admirably for a compass, but he could maintain a reasonably straight line toward that part of the Park’s border the terror beam would cross.

They moved doggedly over mountain-flanks and up valleys, and once they followed a winding hollow for a long way because it led toward their destination without demanding that they climb.  It was in this area that, pushing through brushwood beside a running stream, they came abruptly upon a big brown bear.  He was no more than a hundred feet away.  He stared at them inquisitively, raising his nose to sniff for their scent.

Lockley bent and picked up a stone.  He threw it.  It clattered on rocks on the ground.  The bear made a whuffing sound and moved aggrievedly away.

“I’d have been afraid to do that,” said Jill.

“It was a he-bear,” said Lockley.  “I wouldn’t have tried it on a she-bear with cubs.”

They went on and on.  At mid-morning Lockley found some mushrooms.  They were insipid and only acute hunger would make them edible raw, but he filled his pockets.  A little later there were berries, and as they gathered and ate them he lectured learnedly on edible wild plants to be found in the wilderness.  Jill listened with apparent interest.  When they left the berry patch they swung to the left to avoid a steep climb directly in their way.  And suddenly Lockley stopped short.  At the same instant Jill caught at his arm.  She’d turned white.

They turned and ran.

A hundred yards back, Lockley slackened his speed.  They stopped.  After a moment he managed to grin mirthlessly.

“A conditioned reflex,” he said wryly.  “We smell something and we run.  But I think it’s the old familiar terror beam that crosses highways to stop men from using them.  If it were a portable beam projector with somebody aiming it, we wouldn’t be talking about it.”

Jill panted, partly with relief.

“I’ve thought of something I want to try,” said Lockley.  “I should have tried it yesterday when I first smashed my watch.”