The standard routine was that he would bring out several animals, not putting one away before the other was let loose. Letterman would express concern that things were out of control. Jack would suggest that Letterman hold something, Letterman would refuse. Jack would offer assurances that things were under control, which were often unconvincing.
Letterman would make snide comments about Jack. Suggesting that he might not be the director of the Columbus Zoo, or even suggesting that Columbus did not have a zoo.
Jack Hanna often seemed like something of an airhead. Jack Hanna is very handsome, but at times one suspected this might be his only qualification.
But what I will focus on is Jack Hanna's surprising ignorance of basic biology.
Letterman asked Jack if a scorpion was an insect. Jack said he didn't know. A scorpion is not an insect, it is an arachnid. Other arachnids include spiders and ticks.
In another show Jack informed Letterman that arthropods are insects, no insects are arthropods.
Jack brought on a Rhea from South America and informed Letterman and the audience that it is the third largest land bird. Small mistake, it is forth, behind the African Ostrich, and Australia's Emus and Cassowaries. I think he, or his staff failed to note that Cassowaries are bigger than the Rhea.
I should have started this earlier, because their were more mistakes he made that I forgot.
At any rate this is something of an experiment. If there is interest I may extend the list.