Everything in this movie went realistic. But I think the rehearsals Mr.Chow and Mrs.Chan do isn't convincingly realistic. I mean, these scenes are well directed so that the transformation from one scene to another went smoothly and I enjoyed it while watching. But would anybody do rehearsals in real situations in real life? Isn't it kiddish?!
The primary factor in the rehearsal scenes is its connection to the recurring theme of identity, how each of the characters represent themselves. Chow and Mrs Chan clearly felt weakened by the revelation that their spouses were cheating. Therefore the rehearsal scenes gave them both a chance to construct an alter - egos which rids them of their self-conscious weaknesses.
"I'd rather be hated for who I am, than loved for who I am not".
Yeah I didn't find it particularly unbelievable either.. Particularly because they knew neither of them really had the courage to leave their spouse and move on with each other.. It allowed them to get out those feelings of frustration without actually throwing their lives into complete turmoil.