"Peter Pan Live" star Allison Williams stopped by "The Tonight Show" on Monday to give the late night host a flying lesson.
"The coolest thing is the first time you go up into the air," the actress said. "I've watched a couple of people do it the first time and...everyone has the same expression on their face, which is just utter joy, and then a couple seconds later, pain. It's a harness. It's pretty uncomfortable."
"But I just love watching people take flight for the first time. Would you like to fly right now?" she asked Fallon.
Jimmy was ready to go ... with his Peter Pan hat on!
As the "Girls" star helped Fallon strap on his harness, she suggested he turn away from the audience to adjust ... down there. "I think my bits are where my bits should be," Fallon joked.
"How's that feel?" she asked. "Oh, just wonderful!" he quipped.
Watch the flying lesson above, including when an airborne Fallon sings, "I'm flyiiiiiiiing, I'm flyiiiiiiiing, I am Peter Pan!" (Sorry, Jimmy, but we're afraid that's Allison's title!)