To give an injection, a trainer gives a word or hand signal, and the gorilla will put its shoulder up to the mesh barrier. The trainer will show the gorilla the needle, perhaps giving the ape's shoulder a test touch with their finger or a stick. Then, after a quick stick with the needle, the newly vaccinated ape gets an apple or banana as a treat.
The process doesn't go smoothly every time.
"We do have one who's not particularly fond of doing it. So at that point, it becomes sort of a sneak attack," Jackle said.
To many people, this scenario may sound similar to the last time they took themselves or their children to the doctor for a flu shot. Jackle, who also volunteers at human flu clinics, said the two scenes match in more ways than one.
"It's very similar, especially in dealing with children. There's a lot of coaxing and bribing with lollipops," Jackle said.