A guy who lived very close to his local zoo, and was well known to the staff was wandering around one day when he came to the wildebeest exhibit. He didn't see the usual resident of the enclosure, and and asked a keeper where it was. The keeper told him that the animal was getting on in years, and was either going to be sent to a retirement pasture or possibly put down.
   This made the man kinda sad, and on an impulse he asked if it would be possible to adopt it. The keeper said that that was highly regular, but it sounded like a good idea and he would take it up with the management of the zoo.
   Amazingly, the committee agreed and quietly arranged for the man to have the animal brought to his yard, which was quite spacious and fenced. Well, the man and the wildebeest really bonded, and the guy wondered if he could train his new companion like he had done with a border collie he once had. So he spent several months trying to get it to sit down, lay down on the ground, roll over and even beg for its dinner. Sadly, it was all to no avail, and after a while he gave up, reminding himself of an old saying he once heard.

"You can't teach an old Gnu dog tricks."