Life many years before K4, I flew for Guyana Airways in South America. We would often carry potential pet animals north. Somewhat legal, since we had export certificates, but still something that would never be tolerated now.
About abeam GTK, heading to MIA, I felt something climbing on my leg. After a few excursions from straight and level, I discovered that it was a baby howler monkey. I took a walk back into the main deck and found that one of the monkeys had escaped from his cage and figured out how to open the other cages, emancipating all manner of exotic life to roam free on the plane. When we landed in MIA, we had to close up the plane and have Ag and Animal Services come to round up the suspects and put them back in their cages.