Paddy bought two horses and could never remember which one was which.
To help him work out which was which, he cut the tail off one. This worked well until the other horse lost his tail when it got caught in a bush and Paddy could no longer tell them apart.
His mate Mick suggested he notch the ear of one of the horses. This worked well too until the other horse caught his ear on barbed wire and Paddy could no longer tell them apart.
Mick then suggested to Paddy that he measure both the horses for their height.
Paddy was delighted to discover that the black one was two inches taller than the white one.