Lucentio arrives in Padua to study with his servant Tranio. Baptista refuses to let Bianca marry before her elder sister Katherina and seeks tutors for Bianca. Her suitors, Gremio and Hortensio, agree to find Katherina a husband. Lucentio falls in love with Bianca and plans to approach her as a tutor. He exchanges clothes with Tranio, who will impersonate him and join the suitors. Lucentio orders Biondello to serve Tranio as his master, claiming that the disguise protects him after killing a man. Watching the play, Sly says he wishes it were finished.
What does Petruchio order Grumio to knock on?