Franco, 36, stopped by Tonight after the final showing of his Broadway play Of Mice and Men, and caught up with Fallon, 39, who decided to test the actor's movie knowledge.
"James, you've been in a lot of movies—would you say that you know a lot about movies?" Fallon questioned.
"I think I know a fair amount about movies," Franco asserted.
"Do you think you know enough about movies that you'd be able to summarize them in just five seconds?" Fallon shot back.
Franco stayed confident, saying, "I think I'm going to be able to."
He was then tested with the "5-second summaries" game, in which he had to describe a variety of films in just a few brief moments. Franco failed his first attempt, using the word "pie" to explain American Pie, and went on to blur the lines of the rules as he went forward.
Fallon made a stronger attempt with his description of "a bunch of girls [who] send slacks to each other in the mail" for The Sisterhood of the Traveling Pants.
Watch Franco and Fallon try 5-second summaries in the video above!