It had not been much of a walk, for speed or for fun. For the
humans went ridiculously slowly, and had an eccentric way of
bunching together, every now and again, and then of stringing out
into a shambling line. Still, it was a walk, and therefore better
than loafing behind in the trenches. And Bruce had kept his
noiseless place at the Sergeant's heels.

Then--long before Mahan heard the approaching tramp of feet--
Bruce caught not only the sound but the scent of the German
platoon. The scent at once told him that the strangers were not
of his own army. A German soldier and an American soldier--
because of their difference in diet as well as for certain other
and more cogent reasons--have by no means the same odor, to a
collie's trained scent, nor to that of other breeds of war-dogs.
Official records of dog-sentinels prove that.

Aliens were nearing Bruce's friends. And the dog's ruff began to
stand up. But Mahan and the rest seemed in no way concerned in
spirit thereby--though, to the dog's understanding, they must
surely be aware of the approach. So Bruce gave no further sign of
displeasure. He was out for a walk, as a guest. He was not on
sentry-duty.

But when the nearest German was almost upon them, and all twelve
Americans dropped to the ground, the collie became interested
once more. A German stepped on the hand of one of his newest
friends. And the friend yelled in pain. Whereat the German made
as if to strike the stepped-on man.