Mark Ruffalo is not what we'd call an expected Incredible Hulk -- but that doesn't mean that the actor wasn't great in 'The Avengers' or that we can't wait to see more of him in 'Avengers 2' or even that he's not fully aware that his looks don't scream "HULK MAD."

Ruffalo took to the 'Late Show' last night to chat with host David Letterman about all sorts of Avengers-related things, a boring-sounding premise that's elevated by Letterman's complete lack of knowledge on the Marvel property (though he certainly sounds interested in learning more) and Ruffalo's grace in trying to explain what Hulk is and what Hulk does.

And, yes, he took pains to properly imitate what it looks like when he Hulks out. Letterman, of course, responded in kind.

'Avengers 2' opens in theaters on May 1, 2015.