When Constance enters the story of Othello, she messes with the narrative. Trying to help, she ends up at risk when Desdemona begins to suspect Constance is a witch seducing Othello. Iago fuels this, as he is angry Constance interrupted his plot. In act 2, scene 2, Desdemona tells Iago

Thou wilt instruct me in the manly work
of sword-play; doubtless she is expert there,
for all her lack-a-liver timid show.

Constance, of course, is unaware that Desdemona has turned against her, so when Iago and Desdemona enter sword-fighting and Iago disarms Desdemona, Constance picks up the sword and thrusts at Iago, "poised to skewer him." Desdemona stops her, claiming "twas all in sport," and Constance hands the sword back. Constance is surprised by the adrenaline rush:

I saw a flash of red before my eyes.
I felt a rush of power through my veins.
I tasted iron blood inside my mouth.
I loved it!

Desdemona points her sword at Iago, demanding he show proof of Constance's villainy, and when he produces the pages, she spears Constance's skirt as Constance is whisked away. So we can see in this scene that swordplay is used for deception, for defense, and as a means for the female characters to discover a new power within themselves.

Iago also uses swords in his deception in the original Othello—he convinces Rodergio to attack Cassio and stabs Cassio. However, no women are involved in the swordplay. Desdemona has no means of defending herself when Othello attacks her. We should also note that Othello himself does not engage in fights, instead often trying to stop them. This is different from other Shakespearian heroes who often pick up the sword to get what they want.

Swordplay in Shakespeare's original is shown to be the province of men alone. In Macdonald's reinvented version of the play, she deliberately challenges the presentation of Desdemona as a passive female victim who is weak and unable to do anything about her fate. In the newer version, Desdemona is presented as a bloodthirsty woman who herself shows considerable strength and violence, and is the equal of the men around her. This causes Constance to reflect on her own weak and passive nature:

Boy, Shakespeare really watered her down, eh?...
I wish I were more like Desdemona.
Next to her I'm just a little wimp.
A rodent. Road-kill...

Just as Desdemona's assertive and powerful nature is shown through her confident handling of arms, so too is Constance's change from passive female victim to author of her own destiny indicated when she picks up a sword and defeats Iago in a duel to "save" Desdemona. Swordplay therefore is used as a symbol of female strength and dominance, whereas in Shakespeare's original it is a product of patriarchal society alone, reinforcing the lack of assertiveness of women. 

How is swordplay used differently in Othello and Goodnight Desdemona?

The use of swordplay in both works is minimal yet significant for the tone it sets in each play. The genre of a play is often critical to its meaning. In Othello and Goodnight Desdemona, the genres can be seen through the intent of each sword fight scene and how the main characters act.

Swordplay was used often by Shakespeare, yet Othello is one of the only warriors in his plays that is not seen to fight. In fact, when facing an angry Brabantio in act 1, scene 2, Othello urges others to avoid conflict saying:

Keep up your bright words; for the dew will rust them

The scene progresses with Brabantio angrily insulting Othello, who refuses to rise to the challenge and resort to violence. This scene quickly sets the tone of the play as a tragedy of thought, in which words rather than actions will be important. Othello's refusal to fight is also the first insight into his character, specifically that he has control over the situation. Without establishing this and developing a connection between Othello and the reader, the tragedy would have less impact as Othello's control eventually unravels.

Contrast this to the sword fight in Goodnight Desdemona: a brief fight between Desdemona and Iago in which Constance attempts to intervene and save Desdemona. Important here is the fast pace, ending with Constance being dragged away, and continued contradictions. For example, Constance admires Desdemona's strength shortly before Desdemona turns her anger on Constance herself. This leads to the sense that Constance is not entirely in control of the situation she herself has invented. Shakespeare often placed characters in his comedies as at the mercy of fate, a tactic that is employed in the dreamworld of Goodnight Desdemona.