What does Kate throw out the window at Hortensio and Gremio in The Taming of the Shrew?

In the 1967 movie version of Shakespeare's The Taming of the Shrew (directed by Franco Zeffirelli and starring Richard Burton and Elizabeth Taylor), Katherine—played by Elizabeth Taylor—throws a red fabric-covered, three-legged stool at Hortensio and Gremio out of an upper story window at her father Baptista's house.
Hortensio and Gremio are suitors to Katherine's younger and more amiable sister, Bianca, and Baptista tells them that they can't woo Bianca until a husband has been found for Katherine, the "shrew" of the title of the play.
The stool-throwing in the movie occurs in the scene at the line, "To comb your noodle with a three-legged stool" (1.1.65).
There's no stage direction for Katherine to throw a stool at Hortensio and Gremio anywhere in the same scene in Shakespeare's original play. The stool-throwing was added to the film version by the director or actors.
It's interesting to note that there are very few stage directions in Shakespeare's plays as they've come down to us from the earliest printed versions of the plays. Entrances and exits of the characters and only the most important actions in a scene appear in the original texts. It's not even certain that Shakespeare wrote those stage directions, which might simply have been added at the time of printing.
Two of Shakespeare's most interesting stage directions are, “Enter a messenger with two heads and a hand,” in act 3, scene 1 of Titus Andronicus, and, “He exits, pursued by a bear,” in act 3, scene 3 of The Winter’s Tale.