The 19-year-old sat down with Shawn and fellow star, Javier Bardem.
"I thought I'd test you guys on Australia's saltwater crocodile. My dad had a huge passion for them. We have the longest running crocodile research and, and conservation program in the world," Robert told the actors.
"A crocodile can hold its breath for eight hours. True or false?" he asked, to which both actors guessed "true".
"You got it," Rob said, before asking them if it was true or false that crocs had about 45 teeth.
Shawn and Javier both guessed they had more.
"Wow. You guys know your crocodiles. That's true," the teenager said. "They've got over 60 teeth in their head at any one time."
WATCH: Robert Irwin is emotional after 19th birthday tribute from Steve. (Article continues after video)
His last question was whether it was true or false that crocodiles have one of the strongest jaws of any animal, to which they both correctly guessed true.
At the end of the interview, in his sweet fashion, Rob congratulated the pair on their movie, before saying "see you in Australia hopefully soon".
Rob's croc interview comes soon after a video tribute was curated for his 19th birthday, featuring nostalgic clips of his and his dad's relationship.
When the video ended, Robert wiped away a tear and joked: "Making me cry on my birthday.
"It means the absolute world. I just think it's such a privilege, personally and as a family, to continue the legacy of dad," he added.
"He gave his life, quite literally, for wildlife conservation and to make the world a better place. I just hope he'd be proud."