Fallon reprised his role as brace-face Sara, while Swift played Natalie, a new friend from out of town.
Natalie revealed that she has a Band-Aid collection ("Ew!") and that her mother hasn't let her watch TV "since Miley Cyrus twerked." Needless to say, she hadn't seen Sara's favorite show, ABC Family's Pretty Little Liars. "That's too bad," Sara shouted as she got up in Natalie's face. "You'd like Pretty Little Liars!"
The fast friends then decided to play a round of show and tell. Natalie showed Sara a drawing—before sneezing all over it—and Sara showed her a choreographed dance to Selena Gomez's "Come & Get It." Their dance session was cut short when Sara's stepfather, Gary, interrupted their fun in the basement.
During the Ew! speed round, Natalie weighed in on rice pudding ("Ew!"), yield signs ("Ew!"), airplane mode("Ew!"), breaking up ("Ew!"), getting back together ("Never, ever, ever, ever!") and much more.
When Swift wasn't in character on NBC's The Tonight Show, she confirmed E! News' exclusive scoop that she'll be performing at the MTV Video Music Awards on Aug. 24. "I'm getting a call from MTV later," she said. Asked to divulge details, the 24-year-old singer replied, "We're planning it...and we're planning it."
(E! and NBC are both part of the NBCUniversal family.)