I heard this years ago, but could never remember the penultimate verse!

THE REASON WHY

The dogs they held a meeting; they came from near and far,
Some by automobile and some by trolley car.

Once inside the building they were allowed to look,
Each one took his arsehole off and hung it on a hook.

No sooner were they seated every mother, son and sire,
A scruffy little mongrel jumped up and shouted FIRE!

They ran out of the building; they had no time to look.
Each one grabbed at random an arsehole from a hook.

And that is why a dog will leave a nice fat juicy bone
To sniff the arse of another dog and hope to find his own!