138 
CREATURES OF MYSTERY 
place worth the going. We listened in on everything which 
appeared to bear even a remote relationship to the secret we 
sought. 
During the long years we pursued this one subject we 
chanced to take notice of an article written by someone who 
evidently was familiar with his subject. While it might appear 
to bear little relationship to the subject of just what secret 
means the rattler employed in communicating with his mate, 
yet it was worth noting. The article in question dealt with the 
squeak of the leather-wing bat. The thought was conveyed 
that while young people experience no difficulty in hearing the 
shrill squeak, few past forty ever hear it again, due to a re¬ 
vision downward of the scale of the human ear. This much we 
knew from our own experiences and observations. Even at its 
best the human ear, like the human eye, has its limitations. 
The ear can hear what it was built to hear, and no more. The 
eye can see what it was built to see, and no more. All this, as 
already stated, might be worth something. Maybe not. It was 
not impossible, we reasoned, that the rattler possessed a call 
of some kind readily audible to each other, but outside the 
range of hearing of the human ear. 
Another article written by a noted ornithologist convinced 
us that perhaps there was something of merit to such line of 
reasoning. The blackbird was given as an example. There 
may be ten thousand birds down in a field chirping—making a 
noise which would render the ordinary note inaudible. Yet, 
when their sentry on duty in some tall tree utters a note of 
warning, every single bird in the field hears it as clearly as a 
bugle blast would be heard above the roar of artillery on the 
battlefield. All the birds take wings at the same instant, even 
to the furthermost corner of a large field. Up until recent 
times this was the blackbird’s secret, but is now shared by man. 
No great mystery, after all. Like the leather-wing bat, he is 
capable of uttering a piercing cry so highly pitched that it is 
wholly outside the range of the human ear. 
So year after year we perused all articles and volumes com¬ 
ing before us which held forth the slightest clue to the secret 
we sought. Some entomologist once wrote a highly interesting 
