Once upon a time I'm told
When strange things happened in the world of old
An extraordinary meeting took place
Of dogs from all round the global face.
They all met somewhere near the Golan heights
For a conference on doggy rights.
It took place in a massive hall
Cos anything less would be too small.
As they went in, every dog and pup
took off its coat and hung it up
Then when the conference was over
All the dogs (there were loads called Rover)
Piled outside in lengthy queues
And they couldn't sort out whose coat was whose.
In utter confusion, they all got mixed
And couldn't get the matter fixed,
So each grabbed a coat and made for the door,
Wearing the one which was closest at paw
And, rather than make an almighty stir
They all ended up in another's fir.
Now every time you see dogs meet
Or even passing in the street.
You'll see them have a good old smell
Cos that's the only way they can tell
If its their coat that the other's got.
You may believe this tail or not,
They're only seeking what they treasure
They don't go sniffing bums for pleasure
They want their coats whoever's got 'em
And they can only start at the bottom.
But if they can't find them, that's too tough -
Justice in the world of dogs is ruff.

Terry Donovan

http://www.poemhunter.com/poem/why-dogs-always-smell-each-others-bums/