Mark Ruffalo And Jimmy Fallon Put Their Bromance To The Test With The Best Friends Challenge

"Best friends forever!"

Wednesday was National Best Friends Day, so Tonight Show host Jimmy Fallon decided to celebrate with his celebrity guest Mark Ruffalo. Since Mark has been on the show several times, Jimmy considers them to be pretty good pals. But only the Best Friends Challenge can truly confirm it.

The Best Friends Challenge is a game in which two best buddies have to guess each other's answers to a variety of questions, from favorite sandwich to greatest fear. Mark and Jimmy get pretty passionate in their attempts to prove what good friends they are. They even have a strategy in which they try to give each other visual clues for the right answer.

Whether you think that's cheating or not is irrelevant, because the strategy doesn't work. Jimmy can't figure out that Mark likes peanut butter and jelly sandwiches, and Mark can't decide what Jimmy's favorite physical feature is. They can't even agree on what Mark's biggest fear is. It's surprisingly not "failing the Best Friends Challenge."

Thankfully, they set things right with the final question, directed at Jimmy: "Who is my favorite superhero?" The answer is — you guessed it — the Hulk!

Watch the friendship unfold in the video below: