The mistress, a.k.a. Sabina, now alone, puts the hat back on her head and returns to staring at herself in the mirror.
She remembers once standing next to Tomas, wearing the hat and lingerie, and staring at the mirror. They were both excited by what they saw.
Tomas was fully dressed. The hat symbolized violence against Sabina, because she was nearly naked and her femininity was ridiculed by its masculinity.
The narrator wants to talk some more about the hat. It reminds Sabina of her grandfather and her father. It is a sexual prop with Tomas and marks her individuality. It also has sentimental value for her and Tomas, as it is a testament to their shared past together.
Consider Sabina's life a musical composition; the hat is a motif. Each time it reappears, it does so with a new meaning.
When people meet when they are young, says the narrator, their musical compositions are still developing, and they can exchange motifs, as Sabina and Tomas did.
But if they meet when they are older, as Sabina and Franz, every motif means something different to them. That is why Franz was so confused by Sabina's actions.
And it was not the first time. The narrator has composed an entire lexicon of their misunderstandings.