In what way are Billy's dogs unsual?

There are several things that seperate them from most
dogs, the first is probably their amazing ability to hunt racoons and other animals. 
Obviously part of this is due to the training and the hours that Billy spends working
with them, but as with many things, a part of it is also their innate talents.  They are
absolutely fantastic at chasing down scents and treeing their
prey.

They are also unusual in the rather amazing way they
work together.  They appear to have a clear understanding of each other's limitations
and they play on their own strengths to make sure each hunt is
successful.

In the end, perhaps the other thing that is
unusual about them is their amazing devotion to each other.  Once Old Dan has died from
the wounds he received from the cougar, Little Ann also dies, simply because she has
lost her will to live without him.