The cadets re-enter, and much to their surprise find Christian still alive. The musketeer, deciding that one can now make fun of Cyrano's nose with impunity, tries his hand at the game. Cyrano knocks him down.
Throughout this act, Cyrano's emotions have run the gamut from elation to depression, and the emotions of the audience have followed in close pursuit. In addition to setting up the situation of the play, Rostand has gotten his audience involved with Cyrano, the man. The playwright has made us hope that his main character's dream of love will come true, only to have those hopes dashed to earth. And he has added the irony that Cyrano must not only protect the man who is taking his love from him, but must also help him to win the girl through deception. And so, by the end of the act we are in need of the comic relief furnished by this scene and the two that precede it.
In the previous two scenes, Cyrano is caught in the dilemma of having to accept the insults of the man he has sworn to protect. This internal struggle that goes on as he tries to recount his exploits over Christian's interruptions is a source of high humor for the audience. And the act ends on an even more humorous note when the musketeer misinterprets the situation. Because Cyrano does not kill the musketeer, but simply knocks him down for his insult, it is obvious that Rostand's intention was to end the act on the much-needed light note.