The Avengers cast have spent so much time together that by now, you'd think they'd be able to recognise each other by just a random body part. But apparently they're all so big and muscly that it's just not that simple.
During a few interviews for the Age Of Ultron press tour, Josh Wigler at MTV News put the star-studded superhero squad to the test, by having them play "Guess the Avenger" - from nothing but a photo of their bicep. Some were easy, like Scarlett Johansson's skinnier arm and Chris Hemsworth's trademark "Spock Elbow"; but others like Robert Downey Jr had even Team Chris stumped.
Play along with the Avengers in the hilarious interview below.