Robert Irwin, son of Steve, made his debut on Fallon's show a couple of months ago, and was a massive, massive hit. The host and viewers lapped up Irwin's familiar energy and enthusiasm for animals, and basked in just how similar Robert is to Steve.
He also had great chemistry with Fallon, as he brought out cute animals to lull Fallon into a false sense of security, before bringing out less fluffy beasts. This segment is similar, with adorable baby bears interspersed with legless lizards. It's amusing to see Fallon remain in a state of nervousness regardless of what animal is brought out, and to see an enthusiastic kid reassuring and laughing at a grown man. And Irwin's enthusiasm is infectious.