The Bridesmaids star was discussing her new film Pitch Perfect on the Tonight Show and revealed she had to sing during her audition for the role.
She explained, "It's a comedy but you also have to sing in it. They're like, well, she kind of looks like Adele, but can she sing?" before breaking into Gaga's hit while gyrating for the crowd and slapping her breasts, leaving Leno and fellow guest Bryan Cranston stunned.
Breaking Bad star Cranston decided to join in the fun and clapped along with the audience, before Wilson ended her sing-along by kicking off her shoes and jumping on to her chair.